A 4.40-kg watermelon is dropped from rest from the roof of a 23.0-m -tall buildi

Question

A 4.40-kg watermelon is dropped from rest from the roof of a 23.0-m -tall building and feels no appreciable air resistance.

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

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

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

d)Would the answer in part A be different if there were appreciable air resistance?Yes/No

e)Would the answer in part B be different if there were appreciable air resistance?Yes/No

f)Would the answer in part C be different if there were appreciable air resistance?Yes/No

Explanation / Answer

a) W_gravity = +m*g*h

= 4.4*9.8*23

= 991.8 J

b) Finalkinetic energy = initail potential energy

= m*g*h

= 4.4*9.8*23

= 991.8 J

c) KE = (1/2)*m*v^2

v = sqrt(2*KE/m)

= sqrt(2*991.8/4.4)

= 21.23 m/s

d) No

e) Yes

f) yes.

beacsue when air resistance does negative work, the kinetic decreases.so, final speed also decreases.

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