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:
1
\(3\times 10^6\) Hz
2
\(4\times 10^6\) Hz
3
\(2.4\times 10^7\) Hz
4
\(3.2\times 10^7\) Hz