Question

A boy plant a bomb at a place and started running at 30m/s . After 56 seconds the bomb was blast. In how much time the sound of blast will be listen by boy . If the speed of sound is 450m/s ?

Answer 1

Given

v = Speed of boy = 30 m/s

t = Time taken = 56 seconds

$v_s$ = Speed of sound in air = 450 m/s

To find

The time after which the boy will hear the blast

Solution

s = Distance the boy will be from the bomb at 56 seconds

$s=vt\\\Rightarrow s=30\times56\\\Rightarrow s=1680\ \text{m}$

$t_s$ = The time at which the boy will hear the blast

$t_s=\dfrac{s}{v_s}\\\Rightarrow t_s=\dfrac{1680}{450}\\\Rightarrow t_s=\dfrac{56}{15}\ \text{s}=3.73\ \text{s}$

The sound of the blast will be heard 3.73 seconds later.