Question

A fire station has a horn that sounds a 1750Hz. If you are on your bike moving toward it at 8m/s, what will be the frequency you hear? Assume the air is 20 degrees Celsius.

Answer 1

Since you are moving toward the source of the sound, the frequency of the sound will be shifted according to the formula

`f'= (v+v_o)/(v) f`
where
v is the speed of sound (343 m/s)

`v_o` is the speed of the observer relative to the source, and it is positive when the observer is moving towards the sound (so in this case,
`v_o=8 m/s`)
f=1750 Hz is the original frequency of the sound

Plugging the numbers into the equation, we find that the frequency you will hear is

`f'= (343 m/s+8m/s)/(343 m/s) (1750 Hz)=1791 Hz`