A toy-car, blowing its horn, is moving with a steady speed of 5 m s - 1 , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is 340 m s - 1 the frequency of the horn of the toy car is close to

Question

A toy-car, blowing its horn, is moving with a steady speed of 5 m s - 1 , away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is 340 m s - 1 the frequency of the horn of the toy car is close to, 680 Hz, 510 Hz, 340 Hz, 170 Hz

MARKS App · Accepted Answer

Frequency heard by the observer directly from source f 340 340 - 5 = f 1 Frequency heard by the observer coming after relection from wall f 340 340 + 5 = f 2 Beats frequency = f 1 - f 2 5 = f 340 340 - 5 - 340 340 + 5 ⇒ f = 170 Hz

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