A shot-putter accelerates a 7.3-kg shot from rest to 14 m/s in 1.5 s. What average power was developed?
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This is Giancoli Answers with Mr. Dychko. The average power exuded by the short putter equals the force the short putter applies times the average velocity of the shot. So the force, we'll say, is mass times the acceleration and the acceleration is the change in velocity divided by time and change in velocity is final velocity minus initial velocity; and there is no initial velocity because it starts from rest. So we have the force then is mass times final velocity divided by time. The average velocity is initial plus final divided by 2; initial being zero again so we have average velocity is v f over 2. And we substitute each of these things into the power formula. So we have, in place of f, we are going to write m v f over t. And then in the place of v average, we are going to write v f over 2. And then, I'm multiplying these two factors together; we get m v f squared over 2t. So the average power exuded by the shot putter is 7.3 kilograms—mass of the shot—times 14 meters per second final velocity squared divided by 2 times 1.5 seconds which gives about 4.8 times 10 to the 2 watts of power.
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