question_answer

A bus is moving with a velocity of 5 m/s towards a huge well. The driver sounds a horn of frequency 165 Hz. If the speed of sound in air is 355 m/s, the number of beats heard per second by a passenger on the bus will be:

A)  6                                            

B)  5

C)  3                            

D)  4

Correct Answer: B

Solution :

From the formula \[n'=\frac{\upsilon +{{\upsilon }_{0}}}{\upsilon -\upsilon }.\,n\] \[=\frac{335+5}{335-5}\times 165=170\,Hz\] Hence no. of beats heard per second by the passenger is \[=170-165=5\,\text{beats/sec}\]