Question

A train is moving with constant speed along a circular track. If length of the train is one-fourth of length of circular track then which of the following is/are correct options (Assume that sound source is at engine):

• A. Frequency observed by a passenger who is sitting in the middle of train (equidistant from front and rear end) will continuously increase.
• B. Frequency observed by a passenger who is sitting in the middle of train (equidistant from front and rear end) will remain constant but more than actual frequency.
• C. Frequency observed by a passenger who is sitting in the middle of train (equidistant from front and rear end) will remains constant and equal to actual frequency.
• D. Wavelength observed by the person who is on the rear end of train is more than the actual wavelength of soundwave.

Answer 1

Answer: (C), (D)

The correct options are
C Wavelength observed by the person who is on the rear end of train is more than the actual wavelength of soundwave.
D Frequency observed by a passenger who is sitting in the middle of train (equidistant from front and rear end) will remains constant and equal to actual frequency.

$f_{obs}=\frac{f[v_s+vcos\theta ]}{[v_s+vcos\theta ]}=f$
${\lambda }_{obs}=\frac{v_s+vcos\theta }{f}$
For any observer in train frequency observed is equal to original frequency but observed wavelength is more.