Question

a ball is thrown vertically with a speed  10m/s from the tower 200  meter height and another is thrown vertically downwards with the same speed simultaneously ,the time difference between them reaching the ground in sec  . (g=10m/s)

Answer 1

Ball thrown vertically upwards with a speed 10m/s goes up and stops and comes back to the initial point at the same speed of 10m/s.  This we know.

So both the balls take same time duration from top of tower to the ground on their way down.  But ball 1 travels to the top and comes back to initial point in 2 * t seconds, let us say. Then it takes t sec to reach the top.

v = u + a t       =>      0  =  10 m/s - 10m/sec² * t        => t = 1 sec

So the time difference is 2 seconds.