Question

A boy inside an elevator throws a ball with a velocity of 20 m/s w.r.t lift, if he catches the ball after 2s then the
acceleration of the lift is:
(A) 5 ms 2,down (B) 10 ms 2,up (C) 5 ms-2,up (D) 10 ms 2, down​

Answer 1

Answer:

10 m/s^2 up

Explanation:

as vf-vi=-a't  ..............where a'=g+(acceleration of elevator)

at max height vf=0, time of motion =t= 1 sec

vi=a't

vi/t=g+a

(20/1)-10=a

a=10m/s^2

moving up because if elevator is stationary it will take 4 sec to catch ball

                                 if moving down it will take more than 4 sec

                                 so it is moving up with acceleration of 10m/s^2