Question

a ball is dropped from the top of a tower and simultaneously a ball is thrown up at 40 me. after what time they will collide and height is 100m​

Answer 1

Suppose they will cross each other after time t then the sum of the value of their displacement should be equal to height of tower.

Now displacement of first ball in time t is gt

2

/2

and for second ball it will be ut−gt

2

/2

adding them we will get ut which should be equal to 100meter

so t=2second.