Question

A man drops an apple in the lift. He finds that the apple remains stationary and does not fall. The lift is :

• A. going down with constant speed
• B. going up with constant speed
• C. going down with constant acceleration '$9.8m{s}^{-2}$'
• D. going up with constant acceleration '$9.8m{s}^{-2}$'

Answer 1

Answer: (C)

going down with constant acceleration '$9.8m{s}^{-2}$'

Since the apple remains stationary, so the net force on apple is zero in the frame of man.

That means that the weight of the apple is balanced by the pseudo force acting on the apple.
There is upward pseudo force $=ma$, which has arisen from acceleration ${}^{\prime }{a}^{\prime }$ of the lift in downward direction.

Thus, weight of apple $mg=ma$ (pseudo force)
Hence the lift goes down with constant acceleration (equal to $g$)