The difference between the apparent frequency of a source of soun

Subject

Physics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

The dimensional formula for inductance is

  • [ML2T-2A-2]

  • [ML2TA-2]

  • [ML2T-1A-2]

  • [ML2T-2A-1]


2.

A bullet moving with a speed of 100 ms-1 can just penetrate two planks of equal thickness. Then, the number of such planks penetrated by the same bullet when the speed is doubled will be

  • 6

  • 10

  • 4

  • 8


3.

Two bodies of masses 1 kg and 2 kg have equal momentum. Then, the ratio of their kinetic energies is

  • 2 : 1

  • 3 : 1

  • 1 : 3

  • 1 : 1


4.

The physical quantity having the same dimensions as Planck's constant h is

  • linear momentum

  • angular momentum

  • Boltzmann constant

  • force


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5.

A balloon is rising vertically up with a velocity of 29 ms-1 .A stone is dropped from it and it reaches the ground in 10 seconds. The height of the balloon when the stone was dropped from it is (g = 9.8ms-1)

  • 400 m

  • 150 m

  • 100 m

  • 200 m


6.

SI unit of permittivity is

  • C2m2N2

  • C2m-2N-1

  • C2m2N-1

  • C-1m2N-2


7.

Two equal forces (P each) act at a point inclined to each other at an angle of120°. The magnitude of their resultant is

  • P/2

  • P/4

  • P

  • 2P


8.

When a body moves in a circular path, no work is done by the force since

  • force and displacement are perpendicular to each other

  • the force is always away from the centre

  • there is no displacement

  • there is no net force


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9.

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

  • 1.5 ms-1

  • 12 ms-1

  • 6 ms-1

  • 3 ms-1


D.

3 ms-1

When source approaches the observer, the apparent frequency heard by observer is

              n' = n vv - vs                           ..... (i)

vs = speed of source of sound.

During its recession, apparent frequency

             n" = n vv + vs                             ..... (ii)

Accordingly, n' - n" = 2100 n (given)

  n vv - vs - n vv + vs = 2100 nor  v v + vs - v + vsv - vs v + vs         = 2100or        2vvsv - vs v + vs         = 2100or                        100 vvs         = v2 - vs2

But speed of sound in air, v = 300 m/s

  30000 vs = (300)2 - vs2  vs2 + 3000 vs - 90000 = 0  vs = -30000 ± 300002 + 4 × 900002          = 30000 ± 300062          = 62          = 3 ms-1 9 (taking +ve sign only)


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10.

Curie-Weiss law is obeyed by iron

  • at Curie temperature only

  • at all temperatures

  • below Curie temperature

  • above Curie temperature


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