Question

A car is moving with a speed of $72km/h$ towards a hill. Car blows horn at a distance of $1800m$ from the hill. If echo is heard after $10s$, the speed of sound (in $m/s$) is

• A. $300$
• B. $320$
• C. $340$
• D. $360$

Answer 1

The correct option is C $340$

The speed of the car is $72km/h$
$=72\times \frac{5}{18}=20m/s$
The distance travelled by car in $10s$
$=10\times 20=200m$
Hence, the distance travelled by sound in reaching the hill and coming back to the moving driver
$=1800+(1800-200)$
$=3400m$
So, the speed of sound $=\frac{3400}{10}=340m/s$