Question

A man is watching two trains, one leaving and the other coming with equal speed of 4 m/. If they sound their whistles each of frequency 240 Hz, the number of beats heard by man (velocity of sound in air = 320 m/) will be equal to

(a) 12

(b) 0

(c) 3

(d) 6

Answer 1

Correct option: (d) 6

Explanation:

The apparent frquency of sound of both the trains will be changed.

The apparent frequency of sound of train

For apparent frequency of train going away

When these sounds are heard simultaneously **** is listened.

No. of beats per sec = 243 – 237 = 6.