Two bodies are projected horizontally at the same time from the top of a tower of height $78.4\text{m}$. If their velocities are $30\text{m/s}$ and $40\text{m/s}$ respectively, find the difference between the times taken by them for hitting the ground.

The correct option is D zero
Time taken for body falling from height $h$ with zero initial vertical velocity to hit the ground $=\sqrt{\frac{2h}{g}}$.
Since time of travel is independent of the velocity of projection, therefore difference in time taken by the two bodies is zero.

Hence, option$\left(\text{D}\right)$ is the correct answer.