An observer moves towards a stationary source of sound with a velocity that is one-fifth the velocity of sound. The apparent change in frequency is

Question

An observer moves towards a stationary source of sound with a velocity that is one-fifth the velocity of sound. The apparent change in frequency is (A) zero (B) 5% (C) 20% (D) 0.1%

Tardigrade Admin · Accepted Answer

When the observer is moving towards a stationary source
Apparent frequency

v^{'} = v [\frac{v + v _{0}}{v}]

v^{'} = v [\frac{v + \frac{v}{5}}{v}]

or

v^{'} = \frac{6}{5} v

∴

Change in frequency

= \frac{6}{5} v - v

= \frac{1}{5} v

∴ %

change

= 20%

Q. An observer moves towards a stationary source of sound with a velocity that is one-fifth the velocity of sound. The apparent change in frequency is

zero

5%

20%

0.1%

When the observer is moving towards a stationary source Apparent frequency v′=v[vv+v0​​] v′=v[vv+5v​​] or v′=56​v ∴ Change in frequency =56​v−v =51​v ∴% change =20%

When the observer is moving towards a stationary source
Apparent frequency $v^{'} = v [\frac{v + v _{0}}{v}]$
$v^{'} = v [\frac{v + \frac{v}{5}}{v}]$
or $v^{'} = \frac{6}{5} v$
$∴$ Change in frequency $= \frac{6}{5} v - v$
$= \frac{1}{5} v$
$∴ %$ change $= 20%$