A cyclist with a bell ringing with a frequency of 658.8 Hz drives towards a wall with a speed of 3.18 ms-1. Just before colliding with the wall the cyclist hears beats, due to the bell itself and the reflection of the sound from the wall. What is the frequency of beats detected by the observer? Assume that the velocity of sound in air is 343 ms-1.
fbeat = f1 - f2
The Attempt at a Solution
f'=f(c+v0)/(c-vs)=f(c)/(c-3.18 )=665 Hz
and I am stuck here, I used fbeat = 665 - 658.8 = 6.2 Hz which is incorrect. Could someone help me please?