Question

A siren mounted on a police car (A) chasing car (B) and in same direction emits sound of frequency 180 Hz. A thief is sitting on car (B) and velocity of both cars is equal to 30 m/s. The wavelength of sound received by observer is (velocity of sound 360 m/s)

• A. $1.82m$
• B. $2m$
• C. $2.4m$
• D. $0.28m$

Answer 1

The correct option is A $1.82m$

BY doppler's effect-

Frequency observed$=\left(\frac{V_{sound}-V_{observer}}{V_{sound}-V_{servant}}\right)\times 180=\left(\frac{360-30}{360-30}\right)\times 180$

${\lambda }_{observed}=\frac{360-30}{180}=\frac{330}{180}=1.83m$