Q: From a lift moving upwards with a uniform acceleration a = 2 ms-2, a man throws a ball vertically upwards with a velocity v = 12 ms-1 relative to the lift. The ball comes back to the man after a time t. Find the value of t in second (g=10ms-2).

(a) 4

(b) 2


(d) 6

Ans: (b)

Sol: Time taken by ball to come back to the man is

$\displaystyle t = \frac{2v}{g+a} $

$ \displaystyle t = \frac{2\times 12}{10+2} $

t = 2 sec