Work and Power
1. Describe the conditions that must exist for a force to do work on an object.
2. Calculate the work done on an object.
3. Describe and calculate power.

 Work is the product of force and distance.
 Work requires motion. If there is no movement then no work is done.
 The force must act in the same direction as the object moves. Any part of a force that does not act in the direction of motion does no work on an object.

 Work = Force x Distance

 The Joule (J) is the SI unit of work. It is the work of moving an object with the force of 1 Newton to a distance of 1 meter.

Practice using the Work Formula


 A weight lifter lifts a 1600 N barbell over his head 2.0 meters high.
 W = F x D
W = 1600 N x 2.0 m
W = 3200 J

 Power is the rate of doing work.
Doing work at a faster rate requires more power.
 To increase power:
 1. increase the amount of work done in a given time
 2. do a give amount of work in less time.



 The SI unit of power is the watt (W), which is equal to one joule per second.

How much work does a 25-newton force do to lift a potted plant from the floor to a shelf 1.5 meters high?
100%
A.
52 J
B.
48 J
C.
24 J
D.
38 J
0%
A.
0%
B.
0%
C.
D.

You lift a large bag of flour from the floor to a 1-meter-high counter, doing
100 joules of work in 2 seconds. How much power do you use to lift the bag of flour?
100%
A.
50 W
B.
52 W
C.
48 W
D.
42 W
A.
0%
B.
0%
C.
0%
D.

In which of the following cases is work done on an object?
A.
B.
C.
D.
Pushing against a locked door.
Suspending a heavy weight with a strong chain.
Pulling a trailer up a hill.
Carrying a box down a corridor.
0%
A.
4%
B.
83%
C.
13%
D.