Question

A stone is dropped into a deep well and is heard to hit the water 2 s after being dropped. Determine the depth of the well. Assume no time delay in stone hitting the water and sound being heard. Take $a=10m{s}^{-2}$.

• A. 10 m
• B. 20 m
• C. 30 m
• D. 40 m

Answer 1

The correct option is B 20 m

Given, initial velocity u = 0, acceleration $a=10m{s}^{-2}$, time taken, t = 2 s.
Let the depth of the well be 's'.
Using the second equation of motion,
$s=ut+\frac{1}{2}a{t}^2$
$s=0+\frac{1}{2}\times 10\times 2\times 2=20m$
Hence, depth of the well = 20 m.