A transparent lift `A` is going upwards with velocity `20 ms^-1` and retarding at the rate of `8 ms^-2`. Second transparent lift `B` is located in front of it and is going down at `10 ms^-1` with retardation of `2 ms^-2`. At the same instant a bolt from the ceiling of lift `A` drops inside lift `A` Height of car of lift `A` is `16 m`. Find the time taken by boly to hit the floor of `A`.

Options

A. 2 s
B. 3 s
C. 4 s
D. 6 s

Answer

C

Explanation

In the ref. frame of A :
`V_(b//A) = 0, a_(b//A) = g - a_A = 2m//s^2 darr`
`S_(b//A) = 16 m darr`
`T = sqrt((2 S_(b//A))/(a_(b//A))) = sqrt(((2 xx 16)/(2))) = 4 s`.