Two balls are projected horizontally from the top of a building simultaneously with velocities $15m{s}^{-1}$and $20m{s}^{-1}$ respectively, then the ratio of times taken by them to reach the ground is :

The correct option is D 1:1
Since the balls are thrown horizontally , their initial vertical velocities are zero. Therefore they have same initial vertical velocity and acceleration ($g$),
$v_y=u_y+at$
$v_y=gt$
$g$ is same for both the objects and hence the velocities are also same for a time '$t$'.

Therefore both particles take same time to reach the ground.

Hence, the ratio is $1:1$.