Question

Two ball are thrown simultaneously, A vertically upward with a speed of 20m/s from the ground , and B vertically downward from a height of 40m with the same speed along the same line of motion . At what point do two balls meet

Answer 1

Let h be the distance from the ground where the collision takes place.

Distance from top of tower up to the collision point =40-h

Let collision took place after time t then:

For ball A

$h=20t-\frac{1}{2}gt^2……(1)$

For ball B

$40-h=20t+\frac{1}{2}gt^2……(2)$

Adding (1) and (2) we get

40=40t

Therefore t=1 sec

Putting value of t in (1) we get

$h=(20×1)-(\frac{1}{2}×9.8×1^2)=15.1m$

$( taking :g= 9.8 m /s^2)$

h=15.1 metres

Therefore the two ball meet at 15.1m above the ground