A simple pendulum is suspended from the ceiling of a lift . When the lift is at rest its time period is T. With what acceleration should the lift be accelerated upwards in order to reduce its period to `T//2`? (g is acceleration due to gravity ).

Options

A. 4g
B. g
C. 2g
D. 3g

Answer

D

Explanation

`T=2pisqrt((l)/(g))`.
`T'=(2pi)/(2)sqrt((l)/(g))rArrT'=2pisqrt((l)/(4g))`. The lift should be accelerated by 3g upwards because the total accelerating g+3g pseudo acceleration