**MHT–CET
2004**

*1*. A source is moving towards
observer with a speed of 20 ms^{-1} and having frequency 240 Hz and
observer is moving towards source with a velocity of 20 ms. What is the
apparent frequency heard by observer, if velocity of sound is 340 ms?

**(A) 270 Hz**- (B) 240 Hz
- (C) 268 Hz
- (D) 360 Hz

**MHT-CET
2007 **

*2*. If a source emitting waves of
frequency f moves towards an observer with a velocity v/4 and the observer
moves away from the source with a velocity v/6, the apparent frequency as heard
by the observer will be (where, v = velocity of sound)

- (A) 14/15 f
- (B) 14/9 f
**(C) 10/9 f**- (D) 2/3 f

**MHT-CET
2008**

*3*. An observer moves towards a
stationary source of sound, with a velocity one-fifth of the velocity of sound.
What is the percentage increase in the apparent frequency ?

- (A) Zero
- (B) 0.5%
- (C) 5%
**(D) 20%**

**MHT–CET
2015
**

*4*. The pitch of the whistle of
engine appears to drop to (5/6)^{th} of original value when it passes a
stationary observer. If the speed of sound in air is 350 m/s then the speed of
engine is

- (A) 35 m/s
**(B) 70 m/s**- (C) 105 m/s
- (D) 140 m/s

**MHT-CET
2016**

*5*. When the observer moves towards
the stationary source with velocity, 'V_{1}', the apparent frequency of emitted
note is 'F_{1}'. When the observer moves away from the source with velocity 'V_{1}'
the apparent frequency is 'F_{2}'. If 'V' is the velocity of sound in air and
F_{1}/F_{2} = 2 then V/V_{1} = ?

- (A) 2
**(B) 3**- (C) 4
- (D) 5

**MHT-CET
2017**

*6*. The observer is moving with
velocity 'v_{0}' towards the stationary source of sound and then after crossing
moves away from the source with velocity 'v_{0}'. Assume that the medium through which
the sound waves travel is at rest. If 'v' is the velocity of sound and 'n' is
the frequency emitted by the source then the difference between apparent
frequencies heard by the observer is

**(A) 2nv**_{0}/v- (B) nv
_{0}/v - (C) v/2nv
_{0} - (D) v/nv
_{0}

**MHT-CET
2019**

*7*. An observer moves towards a
stationary source of sound with a velocity one fifth of the velocity of sound.
The percentage increase in the apparent frequency heard by the observer will
be

**(A) 20%**- (B) 0.5%
- (C) 10%
- (D) 5%

**MHT-CET 2020**

*8. *The equation of wave motion is y
= 6 sin[12Ï€t** -** 0.02Ï€x + Ï€/2], where x is in m and t in second The
velocity of the wave is

- (A) 400 m/s
- (B) 200 m/s
**(C) 600 m/s**- (D) 100 m/s

*9*. The frequency of a tuning fork
is 220 Hz and the velocity of sound in air is 330 m/s. When the tuning fork
completes 80 vibrations, the distance travelled by the

**(A) 120 m**- (B) 60 m
- (C) 53 m
- (D) 100 m

*10*. If a star appearing yellow
starts accelerating towards the earth, its colour appears to be turned

- (A) suddenly red.
- (B) gradually red.
- (C) suddenly blue.
**(D) gradually blue.**

*11*. A source of sound is moving towards a stationary observer with velocity 'V_{s}' and then moves away with velocity 'V_{s}'. Assume that the medium through which the sound waves travel is at rest, if 'V' is the velocity of sound and 'n' is the frequency emitted by the source, then the difference between the apparent frequencies heard by the observer is

- (A) 2nV V
_{1}/(V_{s}^{2}- V²) - (B) nV V
_{s}/ (V² - V_{s}^{2}) - (C) nV V
_{s}/(V_{s}^{2}- V) **(D) 2nV V**_{s/V² - Vs2)}

*12*. An obstacle is moving towards the source with velocity 'V'. The sound is reflected from the obstacle. If 'C' is the speed of sound and 'Î»' is the wavelength, then the wavelength of the reflected wave

- (A) Î»r = [(C-V)/C]
- (B) Î»r = [(C+V)/C]
**(C) Î»r = [(C-V)/(C+V)]**- (D) Î»r = [(C+V)/(C-V)]

*13. *A progressive wave of frequency 50 Hz is travelling with velocity 350 m/s through a medium. The change in phase at a given time interval of 0.01 s is

- (A) 3Ï€/2 rad
- (B) Ï€/4 rad
**(C) Ï€ rad**- (D) Ï€/2 rad

*14.* A source of sound is moving with constant velocity of 30 m/s emitting it note of frequency 256 Hz. The ratio of frequencies observed by a stationary observer while the source is approaching him and after it crosses him is speed of sound in aim = 330 m/s

**(A) 6 : 5**- (B) 9 : 8
- (C) 5 : 6
- (D) 8 : 9

*15*. A car sounding a horn of frequency 1000 Hz passes an observer. The ratio of frequencies of the horn noted by the observer before and allot panning of the car in 11 : 9. If the speed of sound is 'V', the speed of the car is

- (A) V
**(B) V/10**- (C) V/5
- (D) V/100

*16. *Two monoatomic ideal gases A and B of molecular masses 'm1' and 'm2' respectively, are enclosed in separate containers kept at the same temperature. The ratio of the speed of sound in gas A to that in gas B is given by

- (A) √m1/m2
- (B) m2/m1
**(C) √m2/m2**- (D) m1/m2

*17*. An observer is approaching a stationary source with a velocity (1/4)^{th} of the velocity of sound. Then, the ratio of the apparent frequency heard by the observer to the actual frequency of the source

**(A) 5 : 4**- (B) 2 : 3
- (C) 3 : 2
- (D) 4 : 5

*18.* A bus is moving with a velocity of 5 m/s towards a wall. The driver blows the horn of frequency 165 Hz. If the speed of sound in air is 335 m/s, then after reflection of sound wave, the number of beats per second heard by the passengers in the bus will be

**(A) 5**- (B) 6
- (C) 2
- (D) 4

*19*. A string of mass 0.1 kg is under a tension 1.6 N. The length of the string is 1m. A transverse wave starts from one end of the string. The time taken by the wave to reach the other end is

- (A) 0.50 s
- (B) 0.30 s
**(C) 0.25 s**- (D) 0.75 s

*20*. A train blowing the whistle moves with a constant velocity 'V' away from an observer standing on the platform. The ratio of the natural frequency of the whistle 'n' to the apparent frequency is 1.2 : 1. If the train is at rest and the observer moves away from it at the same velocity 'V', the ratio of 'n' to the apparent frequency is

- (A) 1.52 : 1
- (B) 0.51 : 1
- (C) 2.05 : 1
**(D) 1.25 : 1**

*21*. With what velocity an observer should move relative to a stationary source so that a sound of double the frequency of source is heard by an observer?

**(A) Same as velocity of sound towards the source**- (B) Twice the velocity of sound towards the source
- (C) Half the velocity of sound towards the source
- (D) Same as velocity of sound away from the source

*22. *When the observer moves towards a stationary source with velocity V_{1}, the apparent frequency of emitted note is F_{1}. When observer moves away from the source with velocity V_{1}, the apparent frequency is F_{2}. If V is the velocity of sound in air and F_{1}/F_{2} = 2 then V/V_{1} is equal to

- (A) 6
**(B) 3**- (C) 5
- (D) 4

*23. *A transverse wave is travelling on a string with velocity 'V'. The extension in the string is 'x'. If the string is extended by 50%. the speed of the wave along the string will be nearly (Hooke's law is obeyed)

- (A) (0.9)V
- (B) (1.1)V
- (C) (0.7)V
**(D) (1.22)V**