Question

A bolt of mass 0.2 kg falls from the ceiling of an elevator moving down with an uniform speed of $5 \mathrm {~ms} ^ { - 1 }$. 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 $\mathrm { g } = 10 \mathrm {~ms} ^ { - 2 }$)

• A. 5 J
• B. 10 J
• C. 15 J
• D. 20 J

Answer 1

Answer: (B)

10 J

Answer 2

Here, m = 0.2 kg. v= 5 ms^-1

h = length of elevator = 5m

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) (5m) = 10J