Question 486: Waves

Question

A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4 m s$$-$$1 at an angle of 60o with the source observer line as shown in the figure. The  observer is at rest. The apparent frequency observed by the observer (velocity of sound in air 330 m s$$-$$1), is

Accepted Answer

Here, original frequency of sound, f
0
= 100 Hz
Speed of source V
s
= 19.4 cos 60ÃÂ° = 9.7
From Doppler's formula
$${f^1} = {f_0}\left( {{{V - {V_0}} \over {V - {V_S}}}} \right)$$
$${f^1} = 100\left( {{{V - 0} \over {V - \left( { + 9.7} \right)}}} \right)$$
$${f^1} = 100{V \over {V\left( {1 - {{9.7} \over V}} \right)}} = {{100} \over {\left( {1 - {{9.7} \over {330}}} \right)}}$$
= 103Hz
Apparent frequency f
1
= 103 Hz

Answer

106 Hz

Answer

97 Hz

Answer

100  Hz

Answer

103 Hz

Waves

Choose the correct answer: