A car drives at a speed of 28 m/s along a road parallel to a railroad track. A t

Question

A car drives at a speed of 28 m/s along a road parallel to a railroad track. A train traveling at 11 m/s sounds a horn that vibrates at 300 Hz.

A) If the train and car are moving toward each other, what frequency of sound is heard by a person in the car?

Express your answer to two significant figures and include the appropriate units.

B) If the train and car are moving away from each other, what frequency of sound is heard in the car?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

Here, velocity of sound, V= 331 m/s

Velocity of Source, Vs = 11 m/s

Velocity of Observer, Vo = 28m/s

Original Frequency, N = 300 Hz

Apperant Frequency, N' = ?

(a) Train and car are moving towards each other, i.e, source and observer are approaching each other. So, Apperant frequency will be given by

N' = N* (V+Vo)/(V-Vs) = 300* (331+28)/(331-11) = 300*359/320 = 336.56 Hz

(b) Train and car are moving away from each other, i.e, source and observer are receding each other. So, Apperant frequency will be given by

N' = N* (V-Vo)/(V+Vs) = 300 * ( 331- 28)/( 331+11) = 300* 303/342 = 265.79 Hz

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