For example:
1) If you lift a book, you are doing work on the book. You book gains energy (its height relative to the ground  increases) and you are losing energy (you are burning some calories = chemical potential energy is used ).
A)What kind of energy the  book is gaining:
kinetic energy ? thermal energy ? gravitational potential energy ? nuclear energy ?  
B) If the mass of the book is 2kg and the change is height is 50cm, what is the work done of the book?
hint: i) find the force applied. the earth exerts a force on the book downward (mg) so you need to exert a force upward (mg) to balance it. F = mg
ii) the displacement is the height. convert to meters
iii) use Work = force x displacement. Units are in joule.
C) In this situation, we say: you are doing work against gravity. Why?

2) To do work on an object, the object needs to move in the same direction as the force. Let's say you are pushing really hard on a wall and you are all sweaty.
A) Are you doing work on the wall? (of course the wall won't move), why ?
B) When you are pushing, your muscles move. So you are losing energy. Where did the energy go ?

3) You are pushing a small red wagon with a constant force F = 5N.
A) According to Newton's second Law   F = m ( ∆V/∆T ) :  
the velocity of the wagon _____________________ but the ________________ is constant.
B) Are you doing work on the wagon ?
C) What kind of energy is transfered to the wagon ?
D) If the displacement = 5 m, find the work done on the wagon.


4) Lee pushes a 20kg mass 100 m across a floor with a horizontal force of 80N. A) CAlculate the amount of work Lee does.
B) what kind of energy is transfered to the mass ?

5) THe third floor of a house is 8 m above street level. A) How much work is needed to move a 150kg fridge to the third floor?
(first find the weight)
B) what kind of energy is transfered to the fridge. C) you are doing work against _________________________

6) Stan does 176 J of work lifting himself 0.300m . What is Stan's mass? (find the weight, then the mass)

7) If the force you apply on an object is not in the same direction as the displacement (of the object) , there is no work on the object.
A) if you carry a suitcase around (moving at a constant speed) , are you doing work on the suitcase ? draw the situation.
(ask yourself if the suitcase gets energy: is it moving faster ? is it getting higher ? )
B) A student librarian picks up a 2.2kg book from the floor to a height of 1.25m. He carries the book 8.0m to the stacks and places the book on a shelf that is 0.35m higher . How much work does he do on the book? (draw a cartoon).

8A) watch the movie in class and answers the questions
work and energy video
 Physics: A World In Motion: Work and Energy  (30mn)
on streaming.discovery
quiz:
1) An escalator lift you to a eight of 3m, your mass is 45kg. What is the work done by the escalator ?
(not taking in account the friction)
2) If the elevator lift you to the second floor, what kind of energy do you gain?
3) potential energy is the energy due to the __________ or the _____________ of an object ?
4) In the ride free-falll why the potential energy at the top is not equal to the kinetic energy at the bottom of the track ? What are other form of energy (rather than Kinetic and potential )


8B) A force of 8.00 10² N is needed to push a car across a lot. Two students push the car 40.0m. How much work is done?

9) A worker carried cement blocks , weighting 1.50  10² N (weight = force) each, up a ladder onto a scaffold 8.00 m high. The worker carries them at a rate of 2 blocks per minute. How much work is done by the worker in: A) 10 minutes ? B) 1.00 hr?
(first find the work done to lift 1 block, then the work done to lift 2 blocks in 1 minute )
10) The hammer of a pile driver has a mass for 1.00 10² kg. THe machine's engine lifts it to a height of 5.00m every 10.0s.
A) How much work must the machine do to lift the hammer ? (first find the weight of the hammer then the work done in 10s)
B) How much work does the machine do in 1.00 min?

11) If you apply a force  F on an object over a distance,  the work done W = force x distance.
If you plot  force vs distance you will get a horizontal line if the force is constant:



Along the x-axis, the distance increases by 1m. Along the yaxis, the force increases by 1N.
A) What is the force applied ? F = ___________N
B) what is the total work done ? W= ___________ J
C) the area under the line is ____________ N.m
D) So the work done is the area under the line _________________________

12) Using what you learnt from 11):
observe the following graphs and compute the work done:



WORK DONE = __________________


WORK DONE = _______________

13) If the graph force vs displacement is not made of lines but is a curve.
(see the first image of this web page).
How could you find the work done? (see the first image, above the title)
any idea ?


machines video:
Work, Energy, and the Simple Machine: Compound Machines
on streaming.discovery