A bob of mass 0.3 kg falls from the ceiling of an elevator moving down with a uniform speed of `7ms^(-1)`. If hits the floor of the elevator (length of the elevator `=` 3m) and does not rebound. What is the heat produced by the impact ? Would your answer be different if the elevator were stationary ?

Explanation

Here,`m=0.3kg, upsilon=7m//s, h=` length of elevator `=` 3m
As relative velocity of the ball w.r.t. elevator is zero, therefore, in the impact , only potential energy of the ball is converted into heat energy.
Amount of heat produced `=` P.E. lost by the ball `= mgh=0.3xx9.8xx3=8.82J`
The answer shall not be differenct, if the elevator were stationary as the ball tooo in that case would start from stationary position, i.e. relative velocity of the ball w.r.t. elevator would coninue to be zero.