Potential And Kinetic Energy Worksheet Page 13
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8.2 Power
8.2
In science, work is defined as the force needed to move an object a certain distance. The amount of work done
per unit of time is called power.
Suppose you and a friend are helping a neighbor to reshingle the roof of his home. You each carry 10 bundles of
shingles weighing 300 newtons apiece up to the roof which is 7 meters from the ground. You are able to carry the
shingles to the roof in 10 minutes, but your friend needs 20 minutes.
Both of you did the same amount of work (force × distance) but you did the work in a shorter time.
W
=
F d
×
W
=
10 bundles of shingles 300 N/bundle
) 7 m
=
21,000 joules
(
×
However, you had more power than your friend.
Work (joules)
Power (watts)
=
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Time (seconds)
Let’s do the math to see how this is possible.
Step one: Convert minutes to seconds.
60 seconds
- - - - - - - - - - - - - - - - - - - - - - - -
10 minutes
=
600 seconds (You)
×
minute
60 seconds
- - - - - - - - - - - - - - - - - - - - - - - -
20 minutes
=
1 200 seconds (Friend)
,
×
minute
Step two: Find power.
21,000 joules
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
=
35 watts (You)
600 seconds
21,000 joules
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
=
17.5 watts (Friend)
1 200 seconds
,
As you can see, more power is produced when the same amount of work is done in a shorter time period. You
have probably heard the word watt used to describe a light bulb. Is it now clear to you why a 100-watt bulb is
more powerful than a 40-watt bulb?
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