A 4.25-kg watermelon is dropped fromrest from the roof of a 20.5-m-tallbuilding

Question

A 4.25-kg watermelon is dropped fromrest from the roof of a 20.5-m-tallbuilding and feels no appreciable air resistance. (a) Calculate the work done by gravity on thewatermelon during its displacement from the roof to the ground.


(b) Just before it strikes the ground find the watermelon's kineticenergy?


Just before it strikes the ground find the watermelon'sspeed?
(a) Calculate the work done by gravity on thewatermelon during its displacement from the roof to the ground.


(b) Just before it strikes the ground find the watermelon's kineticenergy?


Just before it strikes the ground find the watermelon'sspeed?

Explanation / Answer

(a) work = force * distance = mgh = 4.25 * 9.80 * 20.5 = 853.8 Joules . (b) by conservation of energy,   work done bygravity = KE of watermelon = 853.8 Joules . (c)    KE = (1/2) mv2         853.8 = (1/2) * 4.25 * v2 .        v = 20.04 m/s

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