Question

A train blowing its whistle moves with a constant velocity u away from the observer on the ground. The ratio of the actual frequency of the whistle to that measured by the observer is found to be 1.2. If the train is at rest and the observer moves away from it at the same velocity, the ratio would be given by

Solution

Correct option is

1.25

 

If the train is going away from the observer, the apparent frequency is

                             

It is observed that V = 1.2 V1. In the second case, the apparent frequency is

                             

Now, from (i) we have  or u = 0.2 v or  Using this in (ii), we get 

SIMILAR QUESTIONS

Q1

A standing wave having 3 nodes and 2 antinodes is formed between two atoms having a separation of 1.21 Å between them. The wavelength of the standing wave is

Q2

A body is executing S.H.M. with angular frequency 2 rad s–1. If the amplitude of the motion is 60 mm, the velocity of the body at 20 mm displacement is

Q3

 

A wave is represented by the equation  

                                  

Where x is in metres and t in seconds. The expression represents

Q4

A stretched string of length 1 m, fixed at both ends, having a mass of  kg is under a tension of 20 N. It is plucked at a point situated at 25 cm from one end. The string would vibrate with a frequency of

Q5

Two bodies M and N of equal masses are suspended from two separate springs of force constants k1 and k2 respectively. If they oscillate with equal maximum velocities, the amplitudes of M and N will be the ratio of

Q6

A sonometer wire is in unison with a tuning fork. Keeping the tension unchanged, the length of the wire between the bridge is doubled. The tuning fork can still be in resonance with the wire, provided the wire now vibrates in

Q7

A source of sound emitting a note of frequency 200 Hz moves towards an observer with a speed v equal to the speed of sound. If the observer also moves away from the source with the same speed v, the apparent frequency heard by the observer is

Q8

The difference between the apparent frequencies of a source of sound as perceived by an observer during its approach and recession is 2% of the actual frequency of the source. If the speed of sound in air is 300 ms–1, the speed of the source is

Q9

A tuning fork of frequency 480 Hz produces 10 beats per second when sounded with a vibrating sonometer string. What must have been the frequency of the string if a slight increase in the tension of the string produces fewer beats per second than before?

Q10

The intensity of sound gets reduced by 20% on passing through a slab. The reduction in intensity on passage through two consecutive slabs is