Question

A bolt of mass 0.2 kg falls from the ceiling of an elevator moving down with a uniform speed of `5 m s^(-1)`. It hits the floor of the elevator (length of the elevator = 5 m) and does not rebound. The amount of heat produced by the impact is (Take `g = 10 m s^(-2)`)
A. 5 J
B. 10 J
C. 15 J
D. 20 J

Answer 1

Correct Answer - B
Here, m=0.2 kg, `v= 5 m s^(-1)`
h = length of elevator = 5 m
As relative velocity of the bolt w.r.t. elevator is zero, therefore, in the impact, only potential energy of the bolt is converted into heat energy.
Amount of heat produced = Potential energy lost by the ball = mgh
`=(0.2 kg) (10 m s^(-2)) (5 m) =10 J`