Question

At an auto race, a member of the pit crew stands beside the track. A car approaches him at 100 m/s and emits a sound at frequency 1100Hz. The air is still and the speed of sound is 340mls. What frequency will the pit crew member hear? A.1560Hz
B.1420Hz
C.1640Hz
D.850Hz

Answer 1

As per the formula of Doppler's effect we know that

$f = f_o\frac{v}{v - v_s}$

now we know that

v = 340 m/s

$v_s = 100 m/s$

$f_o = 1100 Hz$

now we will have

$f = 1100(\frac{340}{340 - 100})$

$f = 1560 Hz$

so the frequency heard by the crew will be approx 1560 Hz