Question

A motor car approaching a cliff with a velocity of 90 kmph sounds the horn and the echo is heard after 20 seconds. Assuming the velocity of sound in air to be 332 ms${}^{-1}$, the distance between the car and cliff when the horn is sounded is :

• A. 3570m
• B. 3580m
• C. 3590m
• D. 3560m

Answer 1

The correct option is A 3570m

$\vartheta =90km/h$$=90\times \frac{1000}{3600}m/s$$=25m/s$

Distances travelled by sound wave for echo is
$2x-\vartheta \left(t\right)=V\times T$
$2x-25\left(20\right)=332\times 20$
$2x=332\times 20+25\left(20\right)$
$x=\frac{332\times 20+25\left(20\right)}{2}$$=3570m$