Question

A rocket is receding away from earth with velocity $0.2c$, where c is the velocity of light. The rocket emits a signal of frequency $4\times {10}^7$Hz. The apparent frequency of the signal produced by the rocket observed by the observer on earth will be:

• A. $3\times {10}^6$ Hz
• B. $4\times {10}^6$ Hz
• C. $2.4\times {10}^7$ Hz
• D. $3.2\times {10}^7$ Hz

Answer 1

The correct option is D $3.2\times {10}^7$ Hz

$V^{\prime }=V(1-\frac{v}{c})$

$=4\times {10}^7(1-\frac{0.2c}{c})$

$=3.2\times {10}^{7}Hz$