question_answer

A toy-car, blowing its horn, is moving with a steady speed of 5 m/s, away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beat per second. If the velocity of sound in air is 340 m/s, the frequency of horn of the toy car is close to:                                                                                     [JEE ONLINE 10-04-2016]

A)  340Hz

B)       170 Hz

C)       510 Hz            

D)      680 Hz

Correct Answer: B

Solution :

[b]

5 beat sec