Question

If a truck with a frequency of 85.0 Hz is traveling toward an observer with a speed of 27.0 m/s, what frequency does the observer hear as the truck approaches?

Answer 1

The observer will hear a higher frequency as the truck approaches due to the Doppler effect.

The formula for the Doppler effect is:

f' = f((v + vo)/(v + vs))

where:
f = frequency of the sound emitted by the source (in Hz)
f' = frequency of the sound heard by the observer (in Hz)
v = speed of sound in air (about 343 m/s at room temperature)
vo = speed of the observer relative to the medium (in this case, the air) (in m/s)
vs = speed of the source relative to the medium (in this case, the air) (in m/s)

Using the given values, we can plug them into the formula and solve for f':

f' = 85.0 Hz * ((343 m/s + 27.0 m/s) / (343 m/s))

f' = 97.6 Hz

Therefore, the observer hears a frequency of 97.6 Hz as the truck approaches.