# [MCQ] Rotational Dynamics MCQ | Rotational dynamics

### [MCQ] Rotational Dynamics MCQ | Rotational dynamics class 12th

i] When seen from below, the blades of a ceiling fan are seen to be revolving anticlockwise and their speed is decreasing. Select the correct statement about the directions of its angular velocity and angular acceleration.
[A] Angular velocity upwards, angular acceleration downwards.
[B] Angular velocity downwards, angular acceleration upwards.
[C] Both, angular velocity and angular acceleration, upwards.
[D] Both, angular velocity and angular acceleration, downwards.
[A] Angular velocity upwards, angular acceleration downwards.

ii] A particle of mass 1 kg, tied to a 1.2 m long string is whirled to perform vertical circular motion, under gravity. Minimum speed of a particle is 5 m/s. Consider the following statements.
P] Maximum speed must be 5 5 m/s.
Q] Difference between maximum and minimum tensions along the string is 60 N. Select correct option.
[A] Only statement P is correct.
[B] Only statement Q is correct.
[C] Both the statements are correct.
[D] Both the statements are incorrect.
[C] Both the statements are correct.

iii] Select correct statement about the formula [expression] of moment of inertia [M.I.] in terms of mass M of the object and some of its distance parameter/s, such as R, L, etc.
[A] Different objects must have different expressions for their M.I.
[B] When rotating about their central axis, a hollow right circular cone and a disc have the same expression for the M.I.
[C] Expression for the M.I. for a parallelepiped rotating about the transverse axis passing through its centre includes its depth.
[D] Expression for M.I. of a rod and that of a plane sheet is the same about a transverse axis.
[B] When rotating about their central axis, a hollow right circular cone and a disc have the same expression for the M.I.

iv] In a certain unit, the radius of gyration of a uniform disc about its central and transverse axis is 2.5−−−√. Its radius of gyration about a tangent in its plane [in the same unit] must be
[A] 5–√
[B] 2.5
[C] 22.5−−−√
[D] 12.5−−−−√
[B] 2.5

v] Consider following cases:
[P] A planet revolving in an elliptical orbit.
[Q] A planet revolving in a circular orbit.
Principle of conservation of angular momentum comes in force in which of these?
[A] Only for [P]
[B] Only for [Q]
[C] For both, [P] and [Q]
[D] Neither for [P], nor for [Q]
[C] For both, [P] and [Q]

X] A thin walled hollow cylinder is rolling down an incline, without slipping. At any instant, the ratio ”Rotational K.E.:
Translational K.E.: Total K.E.” is
[A] 1:1:2
[B] 1:2:3
[C] 1:1:1
[D] 2:1:3
[D] 2:1:3

### [MCQ] Rotational Dynamics MCQ | Rotational dynamics | rotational dynamics class 12

1] The moment of inertia of a body does not depend upon the________
[a] mass of the body
[b] position of the axis of rotation
[c] distribution of the mass
[d] the angular acceleration of the body

2. The SI unit of moment of inertia is________
[a] gram-cm²
[b] kg-m²
[c] kg/m²
[d] kg-m

3. The dimensional formula for moment of inertia of a body is______
[a] L⁰M¹T-²
[b] L²M¹T⁰
[c] L¹M¹T-¹
[d] L⁰M²T-¹

4. The dimensional formula for the radius of gyration of a body is______
[a] L⁰M⁰T⁰
[b] L¹M⁰T⁰
[c] L¹M¹T⁰
[d] L⁰M²T-¹

5. The SI unit of torque is_______
[a] N/m
[b] Nm²
[c] N-m
[d] N²m

6. Which is the axial vector from the following?
[a] Linear Momentum
[b] Torque
[c] Velocity
[d] Acceleration

7. The rotational analogue of force is_________
[a] Moment of Inertia
[b] Angular Momentum
[c] Torque
[d] Angular Acceleration

8. The physical quantity in translational motion, which analogous to torque in rotational motion is________
[a] Mass
[b] Linear Momentum
[c] Force
[d] Work

9. Torque per unit moment of inertia is________
[b] Angular velocity
[c] Angular displacement
[d] Angular acceleration

10. The physical quantity in translational motion, which is analogous to moment of inertia in rotational motion is________
[a] Velocity
[b] Force
[c] Energy
[d] Mass

11. Moment of inertia depends upon________
[a] position of axis of rotation
[b] distribution of particles
[c] mass
[d] all of these

12. If all the ice on the polar caps of the earth melts, due to global warming then the duration of the day will be________
[a] 24 hours
[b] more than 24 hours
[c] less than 24 hours
[d] 12 hours

13. Which of the following types of circular bodies, Same mass and radius will have the largest moment of inertia ?
[a] Solid disc
[b] Cylindrical disc
[c] Ring
[d] Annular disc

14. A flywheel rotating about a fixed axis has a kinetic energy of 225 J when its angular speed is 30 rad/s. What is the moment of inertia of the flywheel about its axis of rotation?
[a] 0.5 kg m²
[b] 0.6 kg m²
[c] 0.8 kg m²
[d] 0.3 kg m²

15. The mass of a flywheel is concentrated near its rim. This is done to_______
[a] decrease its moment of inertia
[b] increase its moment of inertia
[c] increase the strength of the flywheel
[d] increase its linear momentum

16. A wheel of mass 4 kg and radius of gyration 0.4 m is making 300 r.p.m. Its moment of inertia is_______
[a] 6.4 kg m²
[b] 0.64 kg m²
[c] 0.32 kg m²
[d] 64 kg m²

17. Two circular rings A and B of radii nR and R are made from the same wire. The M.I. of A about an axis passing through the centre and perpendicular to the plane of A is 27 times that of the smaller loop B. What is the value of n?

[a] 2
[b] 3
[c] 4
[d] 5

18. When the speed of a flywheel is increased from 240 r.p.m. to 360 r.p.m., the energy spent is 484 J. What is the moment of inertia of the flywheel ?
[a] 4.9 kg-m²
[c] 2 kg-m²
[b] 9.8 kg-m²
[d] 15 kg-m²

19. A torque of 100 N-m acting on a wheel at rest, rotates it through 200 radian in 10s. What is the moment of inertia of the wheel?
[a] 10 kg-m²
[b] 15 kg-m²
[c] 20 kg-m²
[d] 25 kg-m²

20. If  the external torque acting on a body is zero, then its______
[a] angular momentum is zero
[b] angular momentum is conserved
[c] angular momentum is maximum
[d] angular acceleration is maximum

21. When the external torque acting on a system is zero, then there will be conservation of______
[a] total energy
[b] angular momentum
[c] linear momentum
[d] mass

22. When a torque acting on a system is increased, then which one of the following quantities will increases.
[a] linear momentum
[b] Angular momentum
[c] force
[d] Displacement

23. The moment of inertia of a copper disc, rotating about an axis passing through its centre and perpendicular to its plane_______
[a] increases if its temperature is increased
[b] changes if its axis of rotation is changed
[c] increases if its angular velocity is increased
[d] both [a] and [b] are correct

24. when a steady torque acts on a body, the body_______
[a] rotates at a constant speed
[b] continues in its state of rest or of uniform motion along a straight line
[c] gets a linear acceleration
[d] gets an angular acceleration

25. Moment of inertia of a body is considered only in the case of_________
[a] Rectilinear motion
[b] Rotational motion
[c] Curvilinear motion
[d] Translational motion

26. When the external torque acting on a rotating body is zero, the quantity that will remain constant is the_________
[a] linear momentum
[b] angular momentum
[c] force
[d] linear displacement