# The wavelength is 600 cm when the source is stationary. If the source is moving with relative velocity of 60 m/sec towards the observer, then the wavelength of the sound wave reaching to the observer will be (velocity of sound = 330 m/s) Option 1) 98 cm Option 2) 60 cm Option 3) 49 cm Option 4) 120 cm

As we learnt in

Frequency of sound when observer is stationary and source is moving towards observer -

$\nu {}'= \nu _{0}.\frac{C}{C-V_{s}}$

- wherein

$C=$ speed of sound

$V_{s}=$ speed of source

$\nu _{0}=$ original frequency

$\nu {}'=$ apparent frequency

$\nu=\nu_{o}\:.\:(\frac{C}{C-V_{s}})\:\:\:\therefore\frac{\nu}{\nu_{o}}=\frac{C}{C-V_{s}}$

$\lambda\:\propto \frac{1}{\nu}\:\:\:=>\frac{\lambda_{2}}{\lambda_{1}}=\frac{C-V_{s}}{C}=\frac{330-60}{330}=\frac{270}{330}$

$\lambda_{2}=\frac{9}{11}\times 60.0\:cm\:=\:49\:cm$

Option 1)

98 cm

This option is incorrect.

Option 2)

60 cm

This option is incorrect.

Option 3)

49 cm

This option is correct.

Option 4)

120 cm

This option is incorrect.

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