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Waves · Question 50

AIPMT 2004MCQMedium📈 Topic in 0% papers+4−1
1

A car is moving towards a high cliff. The driver sounds a horn of frequency f. The reflected sound heard by the driver has frequency 2f. If v is the velocity of sound, then the velocity of the car, in the same velocity units, will be

  1. v/ 2
  2. v/3
  3. v/4
  4. v/2

Answer

(2) v/3

Solution

Let the speed of the car be u.

Frequency received by the cliff (source moving towards a stationary observer):

f1 = f vv-u

The cliff reflects f1; the driver moves towards it:

f2 = f1 v+uv = f v+uv-u

Given f2 = 2f:

v+uv-u = 2

⇒ v+u = 2v-2u

⇒ 3u = v

∴ u = v3

Answer: (2)

Out of syllabusAIPMT 2004

Keep practising — Waves

2

An observer moves towards a stationary source of sound with a speed 1/5th of the speed of sound. The wavelength and frequency of the source emitted are and f respectively. The apparent frequency and wavelength recorded by the observer are respectively

  1. 1.2f, 1.2
  2. 1.2f,
  3. f, 1.2
  4. 0.8f, 0.8
Out of syllabusAIPMT 2003
3

A wave travelling in positive X-direction with a = 0.2 m, velocity = 360 m s-1 and = 60 m, then correct expression for the wave is

  1. y = 0.2 [2 (6t + x60 ) ]
  2. y = 0.2 [ (6t + x60 ) ]
  3. y = 0.2 [2 (6t - x60 ) ]
  4. y = 0.2 [ (6t - x60 ) ]
AIPMT 2002
4

A whistle revolves in a circle with angular speed = 20 rad/s using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer which is far away from the centre (velocity of sound = 340 m/s)

  1. 385 Hz
  2. 374 Hz
  3. 394 Hz
  4. 333 Hz
Out of syllabusAIPMT 2002
5

The equation of a wave is represented by y = 10-4 (100t - x10 ) m, then the velocity of wave will be

  1. 100 m/s
  2. 4 m/s
  3. 1000 m/s
  4. 10 m/s
AIPMT 2001
6

Two waves having equation x1 = a ( t - kx + 1), x2 = a ( t - kx + 2). If in the resultant wave the frequency and amplitude remain equal to amplitude of superimposing waves, the phase difference between them is

  1. 6
  2. 2 3
  3. 4
  4. 3
AIPMT 2001
7

If the tension and diameter of a sonometer wire of fundamental frequency n is doubled and density is halved then its fundamental frequency will become

  1. n4
  2. 2n
  3. n
  4. n 2
AIPMT 2001
8

A string is cut into three parts, having fundamental frequencies n1, n2, n3 respectively. Then original fundamental frequency n related by the expression as

  1. 1n = 1n1 + 1n2 + 1n3
  2. n = n1 n2 n3
  3. n = n1 + n2 + n3
  4. n = n1 + n2 + n33
AIPMT 2000
9

Two stationary sources each emit waves of wavelength . An observer moves from one source to the other with velocity u. Then the number of beats heard by him is

  1. 2u
  2. u
  3. u
  4. u2
Out of syllabusAIPMT 2000

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