A 4.50-kg watermelon is dropped from rest from the roof of a 20.0-m -tall buildi

ID: 1444323 • Letter: A

Question

A 4.50-kg watermelon is dropped from rest from the roof of a 20.0-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? yes or no

Part E

Would the answer in part B be different if there were appreciable air resistance? yes or no

Part F

Would the answer in part C be different if there were appreciable air resistance? yes or no

A) W=F*d = -mg*-d = mgd = 50*9.8*20 = 9.8*10^3 J

B) By work energy theorem

KEf - KEi = W

Since vi=0 , KEi= 0J

Thus KEf = W = 9.8*10^3

KEf= 1/2mvf^2

9.8*10^3 =1/2*50*vf^2 => 19.8 m/s

D) Yes, because due to air, frictional work is done opposite to the gravity.

E) Yes, because due to air, frictional work is done opposite to the gravity.

F) Yes, because due to air,frictional work is done opposite to the gravity.

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