Question

A stone is dropped in the river from a bridge. The stone takes 1 second to touch the water surface in the river. What is the height of the bridge from the water level?

• A. 9.8 m
• B. 19.6 m
• C. 4.9 m
• D. 1.96 m

Answer 1

Answer: (C)

4.9 m

When particle is dropped from bridge the initial velocity $u$ is zero.

Let the height of bridge from water level is $h$

Then the displacement traveled by particle is $h$.

Acceleration is $g=9.8m/s^2$ downwards.

Then applying second equation of motion:

$s=ut+\frac{1}{2}a{t}^2$ where $a=g$ and $u=0$

then, $h=\frac{1}{2}g{\left(1\right)}^2=\frac{1}{2}\times 9.8=4.9m$

Thus, option C is correct.