### [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.

**Answer:**

**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.

**Answer:**

[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.

Answer:

[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−−−−√

Answer:

[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]

Answer:

[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

**Answer**:

[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

Answer: D

**2. The SI unit of moment of inertia is________**

[a] gram-cm²

[b] kg-m²

[c] kg/m²

[d] kg-m

**Answer**: B

**3. The dimensional formula for moment of inertia of a body is______**

[a] L⁰M¹T-²

[b] L²M¹T⁰

[c] L¹M¹T-¹

[d] L⁰M²T-¹

**Answer**: B

**4. The dimensional formula for the radius of gyration of a body is______**

[a] L⁰M⁰T⁰

[b] L¹M⁰T⁰

[c] L¹M¹T⁰

[d] L⁰M²T-¹

**Answer**: B

**5. The SI unit of torque is_______**

[a] N/m

[b] Nm²

[c] N-m

[d] N²m

**Answer**: C

**6. Which is the axial vector from the following?**

[a] Linear Momentum

[b] Torque

[c] Velocity

[d] Acceleration

**Answer**: B

**7. The rotational analogue of force is_________**

[a] Moment of Inertia

[b] Angular Momentum

[c] Torque

[d] Angular Acceleration

**Answer**: C

**8. The physical quantity in translational motion, which analogous to torque in rotational motion is________**

[a] Mass

[b] Linear Momentum

[c] Force

[d] Work

**Answer**: C

**9. Torque per unit moment of inertia is________**

[a] Radius of gyration

[b] Angular velocity

[c] Angular displacement

[d] Angular acceleration

**Answer**: D

**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

**Answer**: D

**11. Moment of inertia depends upon________**

[a] position of axis of rotation

[b] distribution of particles

[c] mass

[d] all of these

**Answer**: D

**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

**Answer**: B

**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

**Answer**: C

**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

**Answer**: A

**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

**Answer**: B

**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

**Answer**: B

**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

**Answer**: B

**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

Answer: A

**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

**Answer**: D

**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

**Answer**: B

**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

**Answer**: B

**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

**Answer**: B

**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

**Answer**: D

**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

**Answer**: D

**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

**Answer**: B

**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

**Answer**: B

**27. Which is the wrong relation from the following?**

[a] Force = Mass x Acceleration

[b] Torque = Moment of Inertia x Angular Acceleration

[c] Moment of Inertia = Torque x Angular Acceleration

[d] Angular Momentum = Moment of Inertia x Angular Velocity

**Answer**: C

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

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