Ball A is dropped from the building from top .At the same instant ball B is thrown vertically upwards from the ground.when the balls collide,they are moving in opposite directions and the speed of A is twice the speed of B . At what fraction of height of building did the collision occurs.

Ans 2/3

let is the two balls collide at a distance x from the top.

then distance covered by A = x=1/2gt²

V=gt

but t=

v=g = velocity of A

g/2= velocity of b

distance covered by B is = ut