Question

A boy riding on a bicycle going at 12 km h−1 towards a vertical wall whistles at his dog on the ground. If the frequency of the whistle is 1600 Hz and the speed of sound in air is 330 m s−1, find (a) the frequency of the whistle as received by the wall (b) the frequency of the reflected whistle as received by the boy.

Answer 1

The Frequency at Wall is 1616 Hz

Explanation:

• (a) The frequency of whistle received by the wall can be calculated by,

$f = \frac {(v)f_0}{v - v_s}$

Here,

$f_0$ =1600 Hz

$v_s$ = 12 kmph = 3.33$ms^-^1$

v = 330 $ms^-^1$

f = $\frac {(330)1600}{330 - 3.33}$ Hz

f = 1616 Hz

(b) Now 1616 Hz will act as source frequency.

So, $f_0$ =1616 Hz

$v_s$ = 12 kmph = 3.33 $ms^-^1$

v=330 $ms^-^1$

f = $\frac {(330 + 3.33)\times 1616}{330}$ Hz

f = 1632 Hz