If applied torque on a system is zero, i.e.,Τ = 0 , then

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 Multiple Choice QuestionsMultiple Choice Questions

141.

The speed of earth's rotation about its axis is o. Its speed is increased to x times to make the effective acceleration due to gravity equal to zero at the equator. Then x is

  • 1

  • 8.5

  • 17

  • 34


142.

The moment of inertia of a uniform circular disc of radius R and mass M about an axis passing from the edge of the disc and normal to the disc is

  • MR2

  • 12 MR2

  • 32 MR2

  • 72 MR2


143.

Point masses 1,  2,  3  and  4 kg are lying at the points (0, 0, 0),  (2, 0, 0),  (0, 3, 0)  and  (- 2, -2, 0)   respectively. The moment-of inertia of this system about  X-axis  will be

  • 43 kg-m2

  • 34  kg-m2

  • 27  kg-m2

  • 72  kg-m2


144.

The radius of gyration of a body about an axis at a distance 6 cm from its centre of mass is 10 cm. Then, its radius of gyration about a parallel axis through its centre of mass will be

  • 80 cm

  • 8 cm

  • 0.8 cm

  • 80 m


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145.

A wheel of radius 0.4 m can rotate freely about its axis as shown in the figure. A string is wrapped over its rim and a mass of 4 kg is hung. An angular acceleration of 8 rad-s-2 produced in it due to the torque. Then, moment of inertia of the wheel is (g =10 ms-2 )

  • 2 kg-m2

  • 1 kg-m2

  • 4 kg-m2

  • 8 kg-m2


146.

An object start sliding on a frictionless inclined plane and from same height another object start falling freely.

  • both will reach with same speed

  • both will reach with same acceleration

  • both will reach in same time

  • None of the above


147.

Two rigid bodies A and B rotate with rotational kinetic energies E, and E, respectively. The moments of inertia of A and B about the axis of rotation are IA and IB respectively.

If IA = IB2 and  EA = 100 = EB, the ratio of angular momentum (LA ) of A to the angular  momentum ( LB ) of B is

  • 25

  • 5/4

  • 5

  • 1/4


148.

The working principle of a ball point pen is

  • Bernoulli's theorem

  • surface tension

  • gravity

  • viscosity


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149.

Progressive waves are represented by the equation y1 = a sin (ωt - x )  and y2 = bcos (ωt - x ).  The phase difference wave is

  • 0o

  • 45o

  • 90o

  • 180o


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150.

If applied torque on a system is zero, i.e.,Τ = 0 , then for that system

  • ω = 0

  • α = 0

  • J = 0

  • F = 0


B.

α = 0

τ   the torque on a given axis is product of moment of inertia and angular acceleration. 

              τ = I α

    I = moment of inertia

    α = angular acceleration

     If     τ = 0   = 0

     But       I ≠ 0

                 α = 0

When the torque acting upon a system is zero, the angular momentum is constant and hence conserved. This is analogous to the linear counterpart i.e when the force on the system is zero, the momentum is conserved.


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