Question

A car travelling normally towards a cliff at a speed

of 50 m s–1, sounds its horn when it is 0.7 km

away. Taking the speed of sound to be 300 m s–1 in

air, find the time taken for the driver to hear its echo.

A. 0.04 s B. 4.0 s C. 4.7 s D. 28.0 s

Solve in copy.
for 7.5 points.

Answer 1

Answer: (B)  4 sec

Explanation:

Given that,

Speed v= 50 m/s

Speed of sound = 300 m/s

Distance D= 0.7 km

We know that,

$t = \dfrac{2D}{v_{c} +v_{s}}$

$t = \dfrac{1.4\times10^{3}\ m}{(50+300)\ m/s}$

$t = 4\ sec$

Hence, the time taken for the driver to hear its echo is 4 sec.

So, The correct option is (B).

Answer 2

Answer:

Explanation:

Given that,

Speed v= 50 m/s

Speed of sound = 300 m/s

Distance D= 0.7 km

We know that,

t = \dfrac{2D}{v_{c} +v_{s}}

t = \dfrac{1.4\times10^{3}\ m}{(50+300)\ m/s}

t = 4\ sec

Hence, the time taken for the driver to hear its echo is 4 sec.