Question

A man is driving a car at a speed of 72 kmph towards a hill. He sounds the horn and hears its echo after 2 seconds. At what distance from the hill the horn was sounded. (Velocity of sound = 340 m/s)

• A. 340 m
• B. 260 m
• C. 420 m
• D. 390 m

Answer 1

Answer: (B)

260 m

Let the distance from the hill the horn was sounded is d

$v=72$kmph

$v=72\ast \frac{5}{18}=20m/s$

Let the car traveled x distance in 2 sec:

$x=v\ast t=20\ast 2=40m$

Total distance traveled by sound$=d+(d-x)$

$v_s\ast t=2d-40340\ast 2=2d-402d=680+40d=\frac{720}{2}d=260m$

Hence option 'B' is correct.