Question

A man is moving towards a wall with a source of sound in his hand. Frequency of source = 50Hz. Speed of man = 8m/s. If the man sends one pulse of sound, what will be the frequency heard by him after sound reflects off the wall? Speed of sound = 330m/s.

(a) 53.86Hz

(b) 52.48Hz

(c) 51.24Hz

(d) 52.45Hz

I got this question in an international level competition.

My doubt is from Waves in division Waves of Physics – Class 11

Answer 1

The correct option is (b) 52.48Hz

For explanation: First we find frequency heard by wall.

That will be 50(330)/(330-8) = 51.24Hz.

Now, this will act as source and man will be the listener.

So, the frequency heard by the man

= 51.24(330+8)/330

= 52.48Hz.