  # 4-14 Concept of Power

### Lesson List

Power is the measure of the time in which work can be done.  If two people, each weighing 100 pounds, begin to walk a mile, each will use power to complete the walk.  Walker 1 completes the walk in 30 minutes, while walker 2 completes the walk in 60 minutes.  Each walker is the same weight and walks the same distance.  They each have done 528,000 foot-pounds of work.  100 pounds X 5,280 (feet in a mile) equals 528,000 foot-pounds of work.  Power applies to work over time.

The power of an engine is rated in horsepower.  One horsepower is 55 pounds X a distance of 10 feet over one second of time.  Or 550 foot-pounds per second.  Walker 1 must have had more horsepower to complete the walk quicker than walker 2.  Lets use the formula to determine the horsepower of each walker.

Since each walker weighed 100 pounds and each walker traveled a distance of 5,280 feet, each walker did 528,000 foot-pounds of work (100 X 5,280 = 528,000).  But walker one did the work in half the time and most likely had more horsepower.  Let's solve the formula.

 Walker 1:  528,000 foot-pounds divided by 1,800 seconds (30 minutes X 60 seconds) equals 293.33 foot-pounds per second. Walker 2:  528,000 foot-pounds divided by 3,600 seconds (60 minutes X 60 seconds) equals 146.66 foot-pounds per second.

Neither walker had as much horsepower as a horse does during the walk.

Complete the questions below.

Power is the measure of in which work can be done.

Power applies to over .

Horsepower is the divided by .

One horsepower is foot-pounds per second.

If a 200 pound runner completed a mile race in 10 minutes, how much horsepower did the runner put out?
foot-pounds per second

If a 100 pound runner completed a mile race in 10 minutes, how much horsepower did the runner put out?
foot-pounds per second