A stonemason lifts a small boulder weighing Fw = 80 N from the ground onto a height = 1.50 m wall in the time t = 2.0 s.

Using the values in the problem, calculate how much work she does.

What power does she develop in watts?

What power does she develop in kilowatts?

What power does she develop in horsepower?

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  1. work = force * distance in direction of force
    = 80 * 1.5 = 120 Joules

    Hey we know that cold by now
    = 120 Joules / 2 seconds = 60 Watts

    60 watts * 1 kw/1000 watts = 0.06 kw

    0.06 kw * 1.341 hp/kw = 0.08 Hp

    I figure with an electric motor you get about 1 hp per kw after allowing for efficiency

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  2. work=force(height)
    powerWatts= workJoules/timeinSec



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