INDEX CARD

Kinetic energy (joule) = KE = 0.5 mV²
work (joule) = energy transfered in a system = force(N) x distance (m) (if force is perpendicular  displacement, no work is done)
work is done if increase in speed (or decrease) or increase in height (or decrease)
change in energy kinetic = work done
Potential energy (joule) = PE = mgh
weight (N) = mg with g = 9.8m/s/s
Power (watt) = energy delivered in one second = energy/time = work / time
Energy is conserved if there is no friction: KE = PE .
Heat is a form of energy. Energy can change form like PE to KE and heat.
CONVERT to meters, seconds, kilograms

PART I: INTRODUCTION: FORMS OF ENERGY / UNITS/ FOSSIL FUEL VS URANIUM
This PART I  is now a take home.

1) In middle school you learned the different form of energy : thermal energy (heat energy) ,
kinetic energy (energy of motion or energy of movement),  MECHANICAL POTENTIAL ENERGY
 (energy due to position like the energy stored in a stretched or compressed spring, ready to be used, energy of an object above the ground ),
nuclear energy (energy locked in the nucleus, release during fission (atomic bomb, nuclear plant), fusion (in the sun, hydrogen bomb),
(potential)  electrical energy  (like 2 electrons repelling each other, ready to move away from each other)
(potential) chemical energy (energy stored in atomic bonds like the fat in our body, ready to be used or like the energy in fossil fuel
in both cases oxygen burns organic compounds to produce energy, water and carbon dioxide) ...
You have also RADIATION ENERGY carried by electromagnetic waves like the visible light, UV, X-rays...

Use the previous paragraph  to fill the blanks:
A) Suppose you are pushing a block. You push is unbalanced.  You cause the speed of the block to increase. (newton;s second law = the
block ___________ ). Some of your _________ energy (stored as fat/sugar )  is transformed in __________ energy  (the block moves faster, energy of motion).
 In Physics, the work you are doing is a measure of how much energy is being transfered.
Your work causes the block's ____________ to increase. (energy ? mood ? price ? ). Not all the energy you produce goes into accelerating the
block. You are not a very efficient machine. Some goes into _________ energy. (heat).
When your body burns the fat to get energy, in addition to energy it also releases ________ gas  (you breath it out)  and __________ (aslo breathed out, vapor).
The element oxygen O  comes from the ___________ gas you breath in and the elements carbon and hydrogen come from the ________ ___ you are burning as fuel.

When you are burning fossil fuel to produce electricity, the same kind of chemical reaction takes place.
Fuel (hydrogen + carbon) combine with ___________ from the air to produce  energy + _________  (liquid) + _____________ (global warming).
Of course, this reaction is so fast (time is small in F t = m (V2-V1) ) that the fuel  is in fire. In our body, the time is _________
so luckily we don't get in fire.  (if time is small, force is large so it hurts)

B) Inside the sun, fusion reactions take place and this releases a lot of energy. The plants use the ____________ energy of the sun (from nucleus)
 to transform it in _________ energy (stored in the chemical bonds of sugar molecules).
When we eat the plant, we get also _________ energy (stored again in sugar and fat). . When we move around, this energy is transformed
(by burning some fat ) in __________ energy (you move) and in __________________ energy (you get warmer).

C) If you lift a book, you are doing work against the weight of the book. Your ___________ energy (fat) is being transformed into mechanical ____________energy.
(higher the book is from the ground, greater is its _________ energy)

D) At the top of  a hill, a rock has more ____________ energy than at the bottom. If the rock rolls  down all its _____________energy 
is being transformed into _____________ energy (motion)

E) In an electrical plant coal is used to heat water. The water vapor rises and turn a magnet in to a huge circuit (generator). When the magnet turns, electricity is produced. Billion years ago trees transformed the  _____________ energy of the sun (nucleus)  into  __________energy (as sugar, organic compound) stored
in the plants like trees. When the trees  died, they were buried in swamps and didn't decade (no oxygen in swamps). They were changed into coal over the years.
 The coal was  still containing the chemical energy of the plant (organic compounds). When coal is burned in an electric plant the ___________ energy
(organic compound)  is transformed into ___________energy (heat)  . The coal burns in the electric plant, water is heated and the motiom
of the water vapor (kinetic energy) spins a magnet into a coil (electric circuit). THis is how electricity is produced.
. So Kinetic energy of the wheel has been transfered into _____________ energy.
Conclusion: The electrical energy used in your home comes from the Sun ! of course a lot of the original energy was lost because transformed into thermal energy.
 The electric wires get hot, the wheel gets hot... no machine is 100% efficient transforming energy (input)  into another form (output
 machine produces  heat (lost energy for us).
so energy from sun  is transformed   into energy in plants (sugars)  + heat then is tranformed into electricity !   
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The best Physics class = Physics for future presidents by Richard A. Muller, Berkeley College.
The lectures are on-line. (podcasts). here is the first lecture about ENERGY.
the 2) below is taken from the lecture.

2) A) Fill blanks and READ:
Observe the table and comment: (source = Physics for presidents, Richard A. Muller, Berkeley College California)
1 food Calorie = amount of energy it takes to raise one kg of water by one degree Celsius. = 4,200 J
1 can of soda (coka) = 200 food Calories  = _________ joules (1 food cal = 4,200J)  = _______ KJ   (1 KJ = 1 kilo joule = 1000J)
You need 10J to lift 1 kg  (about 2 pounds)  1 meter (1 yard) .(imagine lifting our big 1 kg mass the height of a meter stick.)
So you need _____________ food calories to lift that mass.  (1 food calorie is 4,200J)

FILL THE BLANKS: use: 1 Cal  (food calorie) = 4,200 J         1 Cal = 1.5 TNT    express joules in KJ (1000 J) or million joules=1,000,000 J

object	energy in 1 g in Cal (food cal)	energy in 1 g in Joules	compared to TNT
bullet (1000ft/s)	0.01	42J	0.015
battery (flashlight)	0.01		0.015
TNT	0.651	2,723J	1
Chocolate cookie	5	________	_________
butter	______________	__________	11
gasoline	_____________	42KJ	________
CH4 (methane)	_________________	__________	20
fuel cell (hydrogen gas)	26	_____________	_____________
asteroid (30km/s)	________________	_____________	165
uranium-235	_________________	84 billion J	___________________

B) Observe the table (filled). Which object (for 1g) can produce the most energy ? __________ the least energy ? __________.

C) What do you find the most surprising in this table ?

D) A cookie (1g) has _________ times more energy than 1 g of TNT. So why can't you blow up a building with TNT ? (think Ft = ∆P )

E) A fuel cell (1g) has _________ times more energy than 1 g of gasoline.

F) -How do you extract gasoline energy in a car ?

G) According to the table, 1 g of gasoline produces __________ times more energy than 1 g of battery.
So it means, if you want to use batteries  to run your car (electric car) and still  get the same energy that is generated by gasoline,
you need a mass of batteries ____________ times more important. (for the same energy extracted).
If you car can carry 10 lbs of gasoline. To get the same potential energy, you will need ___________ lbs of batteries !
convert to tons _________. (1 kg = 2 pounds and 1 ton = 1000kg)/.  

3) Did you know ? KWh is another unit for energy. (look at your electricity bill )
A) CAn you convert 1 KWh (kilowatt hour)  in joule ? ( E (J) = watt (W) x seconds (s) )  1KWh = __________________ J
hint: time = 1 hour = _____________s   1KW = 1,000W

B)  horse power was the unit for power in the 19th century. (when the first automobiles were made)
It is the amount of work a horse can do in one second. 1 horsepower = 745W (about 1000W) = 745 J /s
You can illuminate your house (medium one) brightly with 10 bulbs of 100 Watts during 1 second,
How many horse do you need to do the same job in one second ? (take 1 horsepower = 1,000 Watt= 1,000 J/s)
James Watt compared the power produced by car to horse power so it was easier for people to
understand how muc power you could get from a car. a today " wimpy" car is about 50 horse power or 50KW
a " muscle car" is about 200 horse powers.

C)   The Sun delivers 1KW/m² . If you want to use the energy of the Sun to go green and to produce
clean energy, you have to use cells. You will produce 150W per m². (not 100% efficient).
A nuclear plant can produce 50 GW (1 Giga = 1000,000,000) . so the area covered by a solar plant
is ___________ m² = _____________ km²   (hint: 1 km2 = 1,000,000 m² ) = ________ miles² (hint: 1km² = 0.386 mi²)

4)   watt hour (noted Wh)  is another unit for energy.  (instead of the usual Physics unit joules)
1000 watt hour or 1000 Wh is noted 1 KWh (1 kilo watt hour)
1kWh is about 1000 food calories (noted Cal)  (or about the energy deliverd by a horse during 1 hour)
Human being produce heat very much like a regular 100 wattlight bulb.

The energy they deliver in 1 hour is 100 Watt hour or 100Wh
How much is delivered in 24 hours?    How much is that in food calories ?
does that make sense  ? (how manies Calories an adult should get ?)

Note that: power is the rate of flow of energy. (think of water flowing from a faucet. You can feel a bucket (energy) in 1 hour
or 1 second depending on the rate of low). so a 60 watt bulb produces less energy in 1hour than a 100 w bulb.

5) If you bike for 1 hour you spend about 400 Wh
that is ________ food calories or _________ cans of coka.   (hint: 1 Wh is 1 food CAlorie and 1 can of soda is 200 Calories)
Most of this energy is lost into heat and only 100 Wh is used efficiently into moving the bike.

6) 1 m² of solar cells can produce about 1 KW .
How large is an area of cells that produce 1,000,000,000 W ? (1 giga watt) in m²? in km²?
So to have 1 GW power plant based on power energy, you just need 1 km²

7) 1 m² of solar cells produces 1 KW (1000W) . 1 horse power is also 1 KW. (energy produced by a horse in 1 second)
To make a solar car you can cover it with solar cells. let s say you cover the car with 1 m² of solar cells.
Now, today the solar cells are not yet very efficient. 90% of the energy produced is lost to heat.
so you are left with only _________ KW to make the engine work.    
(hint: 10% of 1KW)
Which is _________ horse power.      (hint : 1 horse power = 1 KW)
Do you think it is now realistic to use solar cars ?    (a regular car produces 30 horse powers when not driving too fast).

8) 60 gallons of fuel contained in a plane can produce 900 tons of TNT of energy (source: Physics for future presidents, Richard Muller)
THis is the energy that can destroy a building during a terrorist attack. (9/11)/
The Korean nuclear essay, that frighted so much the American government,  was a " fizzle " and only produced an energy equivalent
to 400 tons of TNT . Which event is more scary ? 

9) you need 30 pounds of fuel to push one pound in space (in a rocket).
Is this very energy efficient ?

10) 1 g of TNT produces about 1 food calorie 1g of gasoline produces about 10 food calorie
but 1 g of radioactive material produces  1000,000 calories
what is the factor between TNT and the radioactive material ?
between the gasoline and the radioactive material ?

11) electricity company charges about 10 cents per KWh.
If we could plug ourself to get our need in energy (2000 food calories per day)
how much we will have to pay the company ? (1 W = 1 food cal)

12) A typical big coal plant willl produce 1 Giga Watt. Convert to Watts in scientific notation.

13) 1 km² of solar cells could produce 1 GW if they were 100% (with sun rays perpendicular to cells).. But they are only about 40% efficient. (the best ones).
How large is the area covered by solar cells to get 1GW ?
So far, the price of solar cells is $10/cm²
What would be the price of such of an installation ? This is too expensive. But there is a trick.
we can use a lense to focus the light from the Sun. 1 foot² =1000 cm² can focus the light on 1cm² of solar cell.
So the area can be divided by 1000. so the price is now ________. but the lense is $10 so the price is ____________.

14) 1 m2 of solar cell could produce 1 KW
so 10,000 cm² = 10 ft² produces 1 KW  = 1 horse power
Let's say you use solar cells to drive a car. Do you think you car can go fast ?
(small car = 50 horse power).
1 watt of solar cell is $3.50 as for now. (2008). You need about 1000 Watt for a house .
Is the price ok ?


15)  Here is an exercise  given for the regent exam in 9th grade. (NY state)
THe table below shows the relationship between the amount of aluminum in a given type of rock
and the energy needed to extract aluminum from that rock.

sample	aluminum content of ore (percent)	Energy needed to extract 1 ton of aluminum (thousands of KWh)
1	3	220
2	5	140
3	10	90
4	20	65
5	30	54
6	40	49
7	50	48

A) the independent variable (manipulated) is ___________, the dependent variable is ____________(responding)

B) as the % of aluminum in the ore increases, the energy to extract ______________

C) plot the points. Title the graph and the axis. Trace the best fit curve.

D) is it a direct or inverse relationship ?

E) ty to find the equation of the function that best fits the data. (hint: it is a power function y = a x^b )
use your TI to find a and b.

F) according to the graph you constructed, how much energy is needed to produce aluminum
from rock that is 15 percent aluminum? express in thousands of kilowatt-hours ?

16) 1 g of coal produces 29KJ
1g of Uranium 235 produces 96 400 000KJ
Find the ratio _________ or about  10^__

17) In a paper on Energy you can read :
1 barrel of crude oil is 35 gallons or 135 kg. convert to pounds ________ (1kg =2.2 lbs)
1 barrel (133kg )  can produce 5.6 10⁹ J (this is called the EE or energy equivalent). That is for 133kg.
Compute the amount of energy produced by 1 g of crude oil = _________ J = ____ KJ
hint: first convert 133kg in g , 1kg = 1000 g. then do your proportion
Is the number you find consistent with the table in 2) ? (check the energy equivalent for 1g of gasoline = ______ J).

The article  says it took 135 years to use the first trillion barrels of oil and we will use the next trillion in 30 years.
Compute the amount of energy used in 135 years and in 30 years (1trillion of barrels) = _________ J.

The world population is 6 10⁹ people. 14 10¹²J of energy is used  per second in the word. That is 14 10¹² Watts. (or 14 terra watts)
How much of energy is used per person on earth per second (unit is watt) = _______ watt. 
1  light bulb is 100 Watt. The equivalent energy used per person and per second in the world is ____light bulbs.

You can find a linear relationship between the wealth of a country and its energy consumption.
Which country is at the highest point (wealthier and greatest energy consumer ?)
which one is second ?            surprisingly, Switzerland is one of the wealthier country but below the line as a energy consumer.
(I suppose banks don't need that much of oil to work). Note that India and china have the highest rate in energy consumption.

Here is a good web site to undertand how energy can be produced by burning fossil fuel

animation: take a bet.

PART II: KINETIC ENERGY - The WORK-ENERGY THEOREM  (if you are a Math person , try without the hints)

1) READ:and fill blanks
Kinetic energy is the energy of motion. The formula is: Kinetic energy = KE = 0.5 m V²
Energy in joule, mass in kg and speed in m/s.
(write that on an index card)

For the kinetic energy of an object to increase, work has to been done on it.  A force has to be applied over a distance.
THat is you need to apply a ____________  F on the object over a ____________ d.
 W = ∆KE or F x d = ∆KE   ∆KE is the change in energy.
∆KE - KE2 - KE1 = final kinetic energy - initial kinetic energy
F in newton, d in meter and ∆KE in joule.
(write that on an index card)

2) A 1600kg car travels at a speed of 12.5 m/s. What is its kinetic energy?

3) Toni has a mass of 45kg and is moving with a speed of V1 = 10.0m/s.
A) find Toni's kinetic energy. Call it KE1 = _____________
B) Toni's speed changed to V2 = 5.0m/s. Now what is her new kinetic energy ? Call it KE2 = _________
C) what is the ratio of the kinetic energies in A and B ? Explain the ratio ?
hint:  ratio = KE1/  KE2  compare to (V1 / V2)

4)  Shawn and his bike have a total mass of 45.0kg. Shawn rides his bike d = 1.80km in t= 10.0 min at a constant velocity V. What is Shawn 's kinetic energy?
hint: first convert minutes to seconds and kilometers to meter. 

5) In the 1950s, an experimental train that had a mass of m = 2.50 10⁴kg was powered across a level track by a jet engine that produced a trust of F = 5.00 10⁵ N for a distance of  d = 509m.
A) Find the work done on the train

B) Find the change in kinetic energy ∆KE ?


C) Find the final kinetic energy of the train if is started from rest.


D) Find the final speed of the train if there were no friction

6) A 14 700N car is traveling at 25m/s. The brakes are applied suddenly, and the car slides to a stop. THe average braking force between the tires and the road is 7100N.  Can you answer this question :How far will the car slide once the brakes are applied? Follow the steps if you need help:
A) What is the change in energy kinetic of the car ? KE2 - KE1. with V2= 0m/s and V1 = 25m/s. Use the formula.

B) The change in kinetic energy is equal to the work done by the brake. There is a transfer of energy between the car and the road. (All the kinetic energy is being transformed into thermal energy) So ∆KE = work done by the brakes = F x d. Solve for d.

E) Suppose now that the initial speed is twice as much. Find the new distance.

F) conclusion : if you multiply your speed by 2, the distance it takes for the car to come to a stop is multiplied by ___________.
If you multiply your speed by 3, the distance is multiplied by ___________
THis is why, you should be very very careful not exceeding speed limit and keeping a good distance with the car in front of you.

7) A 15.0kg cart is moving with a velocity of 7.50m/s down a level hallway. A constant force of -10N acts on the cart, and its velocity becomes 3.20m/s.
A) What is the change in kinetic energy ? ∆KE = __________

B) How much work was done on the cart ? W = __________

C) How far did the cart move while while the force acted ? _________
hint: ∆KE = W   solve for d

8) REmember the formula: F t = m ∆ V
It is not uncommon during the service of a professional tennis player for the racket to exert an average force of 150.0N
on the ball. If the ball has a mass of 0.060kg and is in contact with the strings of the racket for 0.030s, what is the kinetic
energy of the ball as it leaves the racket ? Assume that the ball starts from rest.

hint: Use F t = m ∆ V  with  ∆ V change in velocity
.
9) Imagine a car braking suddenly because of a cat standing on the road.
The automobile brakes convert KE to heat. The frictional force is
doing work and decreases the kinetic energy of the car. (the work is negative because there is a loss of energy).
change in kinetic energy = work done by frictional force over a distance (work-theory theorem)
THat is: 0.5mV_f² - 0.5 mV_i² = force x distance   with Vf=Vfinal = 0
Not matter the speed, we can consider the force the same. (force is in this case a controlled variable). 
We want to compare the distance covered (responding variable or dependent variable) to stop for different speed (manipulated variable or independent variable).
Consider a car or a bike of mass m. 
Suppose , given the road condition and the tires, it takes the car 10m to stop if the speed is 45km/h. (the car skids over 10 meters).



A) Using the green formula (change in kinetic energy = force x distance, force and mass are constants),
Find the distance if the speed is 90km/k (speed is multiplied by 2).

hint: you can write:   (Equation1)   - 0.5 m (45)² = F x 10    and  
                               (Equation 2)    - 0.5 (90)² = F x d2
Do  Eq1/Eq2  to solve for d2

B) Do if you multiply the speed by 2, the skidding distance is multiplied by ____________

C) Find the distance for a speed = 180km/h (4 times faster).

If you multiply the speed by 4, the distance is multiplied by _________________

10) Consider a runner who keeps track of his/her speed , time, calories burnt.
 There is a relationship between the calories you burn (food calories) C , your speed s,  your weight w  and the time t you run/
The relationship is :
calories burnt = C = 0.0021t w s²
t = time in minutes
w =weight of runner in pounds
s =speed in mi/h
A) Suppose the controlled variable (stay constant) s are the weight (w=200lb), the speed (s=5mph) . THe manipulated variable (independent)  is the __________ t 
and the responding variable (dependent)  is the calories burnt C(t).
The relationship becomes C (t) = _________ t     (substitute w and s in the expression)
This relation is __________.  Fill a table of values and graph the relationship.

x = time (min)	y= calories burnt (Food Cal)

B) Supposed now that the controlled variables are the time (t = 10 minutes) and the speed (s=5miles/h)/ The __________ is now the manipulated
variable and the calories is the __________ variable.
The relationship becomes C(w) = ____________w. Is this a linear relationship ? That means, if you double the weight of the person running,
the amount of calories burnt also ________.

C) Now the weight is a controlled variable (w=200lb), the time is a controlled variable (t = 10 minutes). _________ is the manipulated variable
and ___________ is the responding variable.
You have now C(s) = ________________  (substitute t = 10 and w =200, s is the variable now)
Is this a linear relationship ?      The calories depends not on the speed but on the speed ___________. So if you double the speed,
you multiply the calories burnt by __________ !
Knowing the expression for the kinetic energy, is this surprising ?
What king of graph do you get ?
graph it :

speed (m/s)	calories burned
0
2
3
5
6

11) The work-energy theorem tells us that work done by a force can change the kinetic energy of a system. Kinetic energy
varies with the _______ of the speed. When a car brakes ( and stops) , the frictional forces do negative work on the car and
the car loses its kinetic energy. Work done by the friction = force x distance to stop (skidding distance) = change in kinetic energy
or F x d = 0.5 m V²
The skidding distance in ft  depends on the speed (mph) squared.
Some studies have shown that the distance F(x) can be modeled as :
F(x) = 0.051 x² - 0.38 x
F(x) is the distance in ft and x the speed in mph. Conditions are averages. dry road.
Find the skidding distance if the speed is 60mph
Find the skidding distance if speed is 90mph (multiplied by 3)
comment .

12)
the bed of nails:
The video demonstrates several Physics concepts.
1) mommentum is conserved and transfered very much like the cradlle of Newton.
The momentum of the hammer is conservd and transfered to the top board then from the top board to the person then from the person to the
bottom board and from the bottom board to EArth. So the person is not hurt.
2) The energy kinetic of the hammer goes into smashing the block. It translates as force x distance = damage for the block
not the person. So good thing you don't hit directly the top board. the nails would go into the skin.
3) The  remaining energy spread over every nail. (energy = force x distance). so the force is distributed over each nail
and is not enough to pierce the skin.
12) TAKE HOME QUIZ

13) Speed is relative. (see part I of relativity).
So if a missile was to attck the US at a speed of 1000 miles/hour.
Let's say a small peblbe is sent on the way of the missile. (small speed).
From the missile  point of view (as measured in its frame of reference)
the speed of the pebble is __________. So it becomes a projectile able to destroy it.
This is called a " brillant pebble " . because of its relative speed, the pebble as a lot of __________ energy
as measured in the reference frame of the missile. Suck anti missile device are built in Alaska.

PART III GRAVITATIONAL POTENTIAL ENERGY

9)  REad, fill the blanks.
The increase in potential energy of any system is equal to the work done on the system.
If you lift  a  50kg  mass  from the ground to a height of 10m, you are doing work against the weight of the mass.
WEight of the 50kg = _________.       Force you exert on the weight to balance the weight  =___________
So work done by you = W = ____________. You increase the energy of the mass . Some energy has been transfered from you to the mass.
The same way, when you are climbing stairs, you are doing work against __________. You increase your _____________ energy
because you lift you own ___________ a certain height.

The increase in gravitational potential energy of an object is equal to the work done in placing the object  in its final position:
∆PE = PE2 - PE1 = W = Fd
the force = weight = _____________, the displacement is the __________ h, so
If the gravitational energy PE1 is equal to zero when the object is on the EArth's surface, the gravitational potential energy of the object is
PE = _________             (h is the height  above the ground, m is the mass and g is the acceleration due to gravity, about 10m/s/s)


10)  A  5.0kg bowling ball is lifted from the floor to a height of 1.50m . What is its increase in gravitational potential energy?


11) The 200kg hammer of a pile driver is lifted 10.0 m. Find the gravitational  potential energy of the system when the hammer is at this height.


12)  A 60kg shell is shot from a cannon to a height of 4.0  10² m.
A) What is the gravitational potential energy of the earth-shell system when the shell is at this height ?

B) What is the change in potential energy of the system when the shell falls to a height of 2.00 10² ?


13) A person weighing  630N climbs up a ladder  to a height  of  5.0m
A) what work does the person do ?

B) What is the increase in the gravitational p 10)  A  5.0kg bowling ball is lifted from the floor to a height of 1.50m . What is its increase in gravitational potential energy?

14) The 200kg hammer of a pile driver is lifted 10.0 m. Find the gravitational  potential energy of the system when the hammer is at this height.

15)  A 60kg shell is shot from a cannon to a height of 4.0  10² m.
A) What is the gravitational potential energy of the earth-shell system when the shell is at this height ?

B) What is the change in potential energy of the system when the shell falls to a height of 2.00 10² ?

16) A person weighing  630N climbs up a ladder  to a height  of  5.0m
A) what work does the person do ?

B) What is the increase in the gravitational potential of the person at this height ?

C) Where does the energy  comes from to cause this increase in the gravitational potential energy?

17) source: conceptual Physics from Paul Hewitt

A) Suppose the block of mass has a mass m. Show , using PE = ∆mgh = work done to lift the block ,
that the force required to push the block along the inclined place is only one-fifth its weight. (see legend)
hint:Note that the increase in potential energy will be same no matter the way you choose to elevate the block.
So the work done will be the same.
B) If friction between the ice and the place is neglected (ice) , draw the forces acting on the block pushed along the incline plane.
hint: normal, weight and push
C) Using your drawing , Can you see that the girl has to only overcome some of the weight ? (the component of the weight along the plane).
It is like if the weight is diluted. Can you see that the other component of the weight has to balance the normal force ?
D) A machine can multiply your force or just change the direction of your force. In this case, the incline plane is the machine
and it multiplies your force by _________, you are __________ times stronger. The mechanical advantage is __________.

18) Energy = force x distance
In one of his lecture Dr. Muller explained how the towers collapsed during 9/11. 2 things has to be understood.
a) The infrastructure of these towers rely on steele hollow columns. These are very steady and light at the same time.
(you can hold a book using paper rolled up). However, if heated (after an explosion), the steele expands and can bend.
This is how the last floor collapsed. The floor collapsed on the floor below. b) REmember what we learnt about force multiplier/
weight x height = force x distance. If the first floor (given weight) collpases a given height (say 2m), the column of the floor below
are compressed by a few mm. If they don't move by much, the force is multiplied by a huge amount and the columns below  collapse/ Then
it is the domino effect amplified for each floor.

PART IV  CONSERVATION OF ENERGY


The total emery of a closed, isolated system is constant. Within the system, energy can change form, but the total amount of energy doesn't change.  
A system gets energy if work is done on it. The work done is a measure of the amount of energy transfered.

check transfer energy kinetic/elastic potential in a spring.

1) A) If you lift a 45kg book to a height of 10m (above ground)  the work done on the book (against its weight) is
W = _________ J . (work = force x distance, force = weight of the book).
B) In this case, we are considering the system EArth-book.
We ignore friction and we say that the system is : funny ? isolated ? conserved ? angry ?
The total amount of energy: decreases ? stays the same ? increases ? don't know ?
C) The work done on a book increases the ____________ energy of the book. PE = ______J
D) If you drop the book, the potential energy is transformed in ______________ energy.
If we ignore friction PE = ∆KE = _________ J
E) Find the final speed of the book using conservation of energy (see D)
. V2 = _________ m/s. (V1 = 0m/s , the book is at rest at t= 0s)

2) THe KE and PE of a block freely sliding down a ramp are shown in only one place in the sketch. Fill the missing values. 



3)Fill the blanks.



4)



5)

hint: take a short cut. remember kinetic energy varies like the speed squared.
so if you multiply the speed by 2, the energy is multiplied by4. If the speed is multiplied by 3, the energy is multiplied by 9.
if you multiply the speed by 1.5, the energy is multiplied by 1.5 x 1.5 and so forth.

6)

 

7)





8) A 2kg mass is placed on a frictionless track at point A and releases from rest.
(assume the gravitational potential energy of the system is zero at point E.

1) Find the total mechanical energy of the mass. Use g = 10m/s/s
hint: focus on point A
2) Find the PE at point B
3) From 1)and 2) Find the KE at point B
4) From 3) Find the speed of the mass at point B.
5) If you want to find the speed at point C, do you have to go over all the computations again ?
6) Find the speed at E
7) Find the speed at F

9)



In the above diagram, a toy car having a mass of 4.00 E-2 kg starts from rest at point A and travels 3.60meters along a uniform track until coming to rest at point B. (can't go higher)
A) How can you tell that the track is not frictionless? (there is friction between the car and the road)
B) Suppose the PE is 0 at ground level. Find the PE at point A and at point B: PEA = ________________
and PEB = ____________________
C) Find the energy loss between these two points . (Find PEA - PEB)
D) the energy lost has been transfered into thermal enery because of the work of the force of friction. (work = force x distance)
If the car travels a distance of 3.60 meters along the track, find the magnitude of the frictional force acting on the car.
hint: energy lost = work done by friction

10) worksheet


11) To be able to leave the EArth, you need enough kinetic energy to escape Earth gravity.
The potential energy a rocket , of mass m, has on Earth is PE = G m M / R               G is a constant = 6.67 10^-11   and M is the mass of the EArth = 6 10²⁴kg
m is the mass of the rocket and R is the radius of the EArth    R = 6000km = 6 10⁶ m (about).
You need to give the rocket enough kinetic energy to balance this potential energy. To escape the gravity.
The minimum speed is such as : KE = PE
0.5 m V² = G m M / R        
Solve for the escape speed. V = _________ m/s    = _________ km/s = ___________ mph
(1 km/s = 2 237 mph)

Nothing can escape a black hole, not even light, if you come at a distance R or less of it.
R is called the Schwarschild radius. R depend on the mass of the black hole.
You can find the relationship between R and M using conservation of energy.
(we are supposed to use general relativity but in that particular case the classical formula works)
0.5 mv² = G M m / R
or 0.5 v² = G M / R
Consider the Sun 2 10³⁰kg  what its new radius needs to be so it becomes a black hole(if you were to squeeze it).
Compare with its actual size and compare the new density to its actual density, Search on internet its actual radius,


12) Use the speed you found in 11) in m/s
A meteorite that hits the Earth can produce a lot of energy. Let's have an idea how much of energy it will produce.
Imagine a modest meteorite of 1 ton (1000kg) when it reaches the ground. (some of the mass was lost in the atmosphere, melted
away by the friction between the rock and the air).  That's about a car.
Imagine the meteorite comes from infinity and hits the Earth with some  kinetic energy KE (just before reaching ground).
A) Since it comes from very far away (where the PE is 0), the PE is being converted to kinetic energy.
energy when the meteorite hits the Earth = PE = 0.5 mv² ,= ___________  joules (use the speed found in 11) ).
How much TNT is that ? (refer to table above). __________

B) Most of this kinetic energy is lost in to heat + sound + motion of dust when it hits the ground.  
It can do a lot of damage, depending on it s mass. Some say it helped the mass extinction,  65 millions years ago,  of more than 90% of
life on Earth, including the dinosaurs./
Using the table from PART I 2) :
How many grams of Uranium, do you need to produce the same energy ?
How many grams of chocolate cookies ?

13) Maybe you learnt in Chemistry that the temperature of a system (human body, table, air ...) is proportional to the average kinetic energy
of the molecules that make up the system.  So if the kinetic energy of a gas is multiplied by 2, the temperature is also multiplies by _______.
REmember the kinetic energy is 0.5 m V² . m is for the inertia of the molecule (mass). and V is for the average speed of the molecules container in the system.
Let's image a shoe box with ping pong balls and steel balls. (This  a model for a system made of 2 types of molecules.
 heavy molecule of gas like oxygen or Co₂ and lighter molecules like helium). The ping pong balls could be helium and oxygen could be the steel balls.
You shake them at a constant rate.  (the gas molecules are moving, bouncing around).  You give the molecules a given amount of energy.
(so you get a given temperature).
A) Do you think the ping pong and the steel balls have the same speed ? (they have the same kinetic energy 0.5 m V²⁾
Why or why not ?

B) Based on your answer, can you explain why inhaling helium makes your voice higher in frequency ?

(hint: helium is lighter than sir molecules like nitrogen and oxygen. When you speak you put the gas you breath  in motion,
giving them kinetic energy)

14) fill the blanks (source: Paul Hewitt, conceptual Physics, Addison-Wesley)