Rotational Motion Multiple Choice Questions and Answers - Set 02 - ObjectiveBooks

# Practice Test: Question Set - 02

1. Four identical particles, each with mass m, are arranged in the x, y plane as shown. They are connected by light sticks to form a rigid body. If m = 2.0 kg and a = 1.0 m, the rotational inertia of this array about the y-axis is:
(A) 4.0 kg.m2
(B) 12 kg.m2
(C) 9.6 kg/m2
(D) 4.8 kg/m2

2. Two circular disks having the same mass and the same thickness are made from different materials. The disk with the smaller rotational inertia is:
(A) The one made from the more dense material
(B) The one made from the less dense material
(C) Neither — both rotational inertias are the same
(D) The disk with the larger angular velocity

3. The meter stick shown below rotates about an axis through the point marked, 20 cm from one end. Five forces act on the stick: one at each end, one at the pivot point, and two 40 cm from one end, as shown. The magnitudes of the forces are all the same. Rank the forces according to the magnitudes of the torques they produce about the pivot point, least to greatest.
(A) F1, F2, F3, F4, F5
(B) F1 and F2 tie, then F3, F4, F5
(C) F2 and F5 tie, then F4, F1, F3
(D) F2 and F5 tie, then F4, then F1 and F3 tie

4. A cylinder is 0.10 m in radius and 0.20 in length. Its rotational inertia, about the cylinder axis on which it is mounted is 0.020 kg.m2. A string is wound around the cylinder and pulled with a force of 1.0 N. The angular acceleration of the cylinder is:

5. A certain wheel has a rotational inertia of 12 kgm2. As it turns through 5.0 rev its angular velocity increases from 5.0 rad/s to 6.0 rad/s. If the net torque is constant, its value is:
(A) 0.016 Nm
(B) 0.18 Nm
(C) 0.57 Nm
(D) 2.1 Nm

6. A small disk of radius R1 is fastened coaxially to a larger disk of radius R2. The combination is free to rotate on a fixed axle, which is perpendicular to a horizontal frictionless table top. The rotational inertia of the combination is I. A string is wrapped around the larger disk and attached to a block of mass m, on the table. Another string is wrapped around the smaller disk and is pulled with a force F as shown. The tension in the string pulling the block is:
(A) R1F/R2
(B) mR1R2F/(ImR22 )
(C) mR1R2F/(I + mR22 )
(D) mR1R2F/(ImR1R2)

7. A disk starts from rest and rotates around a fixed axis, subject to a constant net torque. The work done by the torque during the second 5 s is __________ as the work done during the first 5s.
(A) The same
(B) Twice as much
(C) Half as much
(D) Four times as much

8. One revolution per minute is about:

9. If a wheel turning at a constant rate completes 100 revolutions in 10 sec its angular speed is:

10. A flywheel of diameter 1.2 m has a constant angular acceleration of 5.0 rad/s2. The tangential acceleration of a point on its rim is:
(B) 3.0 m/s2
(C) 5.0 m/s2
(D) 6.0 m/s2

11. The rotational inertia of a wheel about its axle does not depend upon its:
(A) Diameter
(B) Mass
(C) Distribution of mass
(D) Speed of rotation

12. When a thin uniform stick of mass M and length L is pivoted about its midpoint, its rotational inertia is ML2/12. When pivoted about a parallel axis through one end, its rotational inertia is:
(A) ML2/12
(B) ML2/6
(C) ML2/3
(D) 7ML2/12

13. As a particle starts from rest and moves with constant angular acceleration around a circular orbit, the point of application of the force acting on it does not change. This must mean:
(A) The torque acting on it is increasing in magnitude
(B) The torque acting on it is decreasing in magnitude
(C) The force acting on it is increasing in magnitude
(D) The force acting on it is decreasing in magnitude

14. A thin circular hoop of mass 1.0 kg and radius 2.0 m is rotating about an axis through its center and perpendicular to its plane. It is slowing down at the rate of 7.0 rad/s2. The net torque acting on it is:
(A) 7.0 Nm
(B) 14.0 Nm
(C) 28.0 Nm
(D) 44.0 Nm

15. A wheel is spinning at 27 rad/sec but is slowing with an acceleration that has a magnitude given by 3t2, in rad/s² for t in seconds. It stops in a time of:
(A) 1.7 s
(B) 2.6 s
(C) 3.0 s
(D) 4.4 s

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