correct option is C.
Explanation:
As the source is stationary. And the observer is moving towards the source. It leads to Doppler effect. The frequency measure by the observer will be higher as is it moving towards the source. Lets find out the value of frequency.
The formula for this case is,
[tex]v = v_{o} (1+\frac{v}{c})[/tex]
where
[tex]v_{o}[/tex] = c/λ
λ = wavelength
by putting it in above equation,
v = c/λ ( 1+ v/c)
= [tex]\frac{4.0}{0.8}( 1+\frac{1.0}{4.0} )[/tex]
= 6.3 Hz.
So the correct option is C.
