Question

The bird in fig A drops the stone from a height of 88 m above the water surface. Initially, the stone has zero vertical velocity. How long will it take the stone to reach the surface of the pond? (Assume air resistance is negligible.)

Answer 1

The distance travelled during the free fall is given as follows:

$$d = \dfrac{gt^2}{2}$$

where $g = 9.81m/s^2$ is the gravitational acceleration, $t$ is the time that was taken the stone to reach the surface of the pond. Since $d = 88m$, obtain:

$$t = \sqrt{\dfrac{2d}{g}}\\ t = \sqrt{\dfrac{2\cdot 88}{9.81}} \approx 4.2s$$

Answer. 4.2 s.