an automobile is travelling towards you at a speed 25.0m/s. When you measure the frequency of its horn, you obtain a value of 26Hz. If the actual frequency of the horn is known to be 240Hz, calculate speed of sound in air?

Question

an automobile is travelling towards you at a speed 25.0m/s. When you measure the frequency of its horn, you obtain a value of 26Hz. If the actual frequency of the horn is known to be 240Hz, calculate speed of sound in air?
answer is 325m/s

Henry · Answer

Vs = 25 m/s = Velocity of the source.

F = 260 Hz(NOT 26Hz).

Fo = 240 Hz.

Vr = Velocity of the receiver(person)

F = (V+Vr)/(V-Vs)*Fo = 260 Hz.
(V+0)/(V-25)*240 = 260
240V/(V-25) = 260
240V = 260V - 6500
-20V = -6500
V = 325 m/s.