A 4.70-kg watermelon is dropped from rest from the roof of a 28.0-m -tall buildi

Question

A 4.70-kg watermelon is dropped from rest from the roof of a 28.0-m -tall building and feels no appreciable air resistance.

Part A

Calculate the work done by gravity on the watermelon during its displacement from the roof to the ground.

Part B

Just before it strikes the ground, what is the watermelon's kinetic energy?

Part C

Just before it strikes the ground, what is the watermelon's speed?

Part D

Would the answer in part A be different if there were appreciable air resistance?

Would the answer in part A be different if there were appreciable air resistance?

No

Part E

Would the answer in part B be different if there were appreciable air resistance?

Would the answer in part B be different if there were appreciable air resistance?

No

Part F

Would the answer in part C be different if there were appreciable air resistance?

Would the answer in part C be different if there were appreciable air resistance?

No

Part E

Would the answer in part B be different if there were appreciable air resistance?

Would the answer in part B be different if there were appreciable air resistance?

No

Part F

Would the answer in part C be different if there were appreciable air resistance?

Would the answer in part C be different if there were appreciable air resistance?

Explanation / Answer

Its given that,

the mass of the watermelon = m = 4.7 kg and its resting at a height = h = 28.0 m

(a)The workdone by gravity in this case is simply the change in it PE. At groung h becomes zero, so

Workdone = mg (h 1 - h2) = 4.7 x 9.8 x (28-0) = 1289.68 Joules

(b)The Gravitational potential energy has been converetd to KE So KE = 1289.68 Joules

(c) We already have

1/2 mv2 = 1289.68 which gives us

v = sqrt (2 x 1289.68 / m) = sqrt (2579.36/4.7) =sqrt(548.8) = 23.42 m/s

hence v = 23.42 m/s

Part(d) No, it shouldnt be because all the workdone by gravity is change in PE and PE for a particular mass depends on the changing height (as g and m are constant).

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