Question

A stone is dropped into a lake by a man from a tower of height $500\text{m}$. The sound of the splash will be heard by the man after
[velocity of sound in air $=340{\text{ms}}^{-1}$]

• A. $21.5\text{s}$
• B. $10.5\text{s}$
• C. $11.5\text{s}$
• D. $14.5\text{s}$

Answer 1

The correct option is C $11.5\text{s}$

Time taken by stone to hit lake,
$t_1=\sqrt{\frac{2h}{g}}=\sqrt{\frac{2\times 500}{10}}=10\text{s}$
Time taken by sound wave to reach the man standing at top of tower,
$t_2=\frac{h}{v}=\frac{500}{340}=1.5\text{s}$
So, total time,
$t=t_1+t_2=10+1.5=11.5\text{s}$