question_answer

A and B are two sources generating sound waves. A listener is situated at C. The frequency of the source at A is 500 Hz A, now, moves towards C with a speed 4 m/s. The number of beats heard at C is 6. When A moves away from C with speed 4 m/s, the number of beats heard at C is 18. The speed of sound is 340 m/s. The frequency of the source at B is:          [JEE ONLINE 22-04-2013]

A)        500 Hz            

B)  506 Hz

C)  512 Hz            

D)  494 Hz

Correct Answer: C

Solution :

[c]

Case 1: When source is moving towards stationary listener apparent frequency

Case 2: When source is moving away from the stationary listener

In case 1 number of beats heard is 6 and in case 2 number of beats heard is 18 therefore frequency of the source at B = 512 Hz