Question

At what speed is a car approaching a
stationary observer if he hears the music of
the car radio with a frequency 10% higher
than the actual frequency ? Speed of
sound =340 ms^-1.

Answer 1

Doppler effect is given by formula

$$\frac{\Delta f}{f}=\frac{v}{c}$$

So, the speed of a car

$$v=c\frac{\Delta f}{f}$$

$$=340\:\rm{m/s}\times 0.1=34\:\rm{m/s}$$