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NEET Physics: conservation of angular momentum and its applications Practice Questions

15 free multiple-choice questions on conservation of angular momentum and its applications (Rotational Motion) for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. A solid cylinder rotating about its central axis experiences a change in angular momentum. This change is primarily due to:

    • AChange in angular velocity
    • BChange in linear momentum
    • CChange in mass
    • DChange in energy
    Show answer & explanation

    Correct answer: A — Change in angular velocity

    Angular momentum L=Iω. If L changes, either I or ω (or both) must change. If the cylinder rotates (changes ω), its angular momentum changes unless the rotation is caused by an external torque or internal force acting on the system.

  2. Q2. The moment of inertia of a body depends on the distribution of mass relative to the axis of rotation. Which of the following masses contributes most significantly to the moment of inertia of a rotating object?

    • ATotal mass of the body
    • BMasses distributed far from the axis of rotation
    • CMass of the center of mass
    • DMass of the edge of the object
    Show answer & explanation

    Correct answer: B — Masses distributed far from the axis of rotation

    The moment of inertia depends on mr². Masses further away from the axis of rotation contribute more significantly to the total moment of inertia.

  3. Q3. Which of the following physical quantities is conserved when a system is subjected only to internal forces (no external net torque)?

    • AKinetic Energy
    • BAngular Momentum
    • CLinear Momentum
    • DMechanical Energy
    Show answer & explanation

    Correct answer: B — Angular Momentum

    Angular momentum is conserved if and only if the net external torque is zero. When only internal forces act, the system is isolated from external torques, ensuring that its angular momentum remains constant.

  4. Q4. If the moment of inertia of a rotating object is doubled while its angular velocity remains constant, what happens to its angular momentum?

    • AIt remains the same
    • BIt is halved
    • CIt is doubled
    • DIt is quadrupled
    Show answer & explanation

    Correct answer: C — It is doubled

    Since L = Iω, if I doubles and ω is constant, the angular momentum L must also double.

  5. Q5. A body is rotating with a constant angular velocity. If the moment of inertia of the body is doubled, what happens to its angular momentum?

    • AThe angular momentum becomes four times
    • BThe angular momentum is doubled
    • CThe angular momentum remains the same
    • DThe angular momentum is halved
    Show answer & explanation

    Correct answer: B — The angular momentum is doubled

    Angular momentum (L) is defined as L = Iω. If ω is constant, and the moment of inertia (I) is doubled, the angular momentum (L) must also be doubled.

  6. Q6. In the absence of any external net torque acting on a system, the angular momentum of the system will:

    • ABecome zero
    • BIncrease
    • CRemain unchanged
    • DDecrease
    Show answer & explanation

    Correct answer: C — Remain unchanged

    The principle of conservation of angular momentum states that if the net external torque is zero, the angular momentum (L) of the system remains constant.

  7. Q7. A solid disc is rolling without slipping on a horizontal surface. If the disc is given a small impulse to increase its rotational motion, which quantity remains conserved during this process?

    • AThe angular momentum of the disc
    • BThe kinetic energy of the disc
    • CThe torque applied to the disc
    • DThe linear momentum of the disc
    Show answer & explanation

    Correct answer: A — The angular momentum of the disc

    Since the only external force acting on the system (disc + surface interaction) is horizontal, the net external torque about the center of mass is zero. Therefore, the angular momentum of the disc about its center of mass is conserved.

  8. Q8. A body is rotating under the influence of internal forces only. If there are no external torques acting on the body, what is the state of its angular momentum?

    • AAngular momentum decreases
    • BAngular momentum remains constant
    • CAngular momentum depends on the mass of the body
    • DAngular momentum increases
    Show answer & explanation

    Correct answer: B — Angular momentum remains constant

    The law of conservation of angular momentum states that if the net external torque (τₑₓₜ) acting on a system is zero (τₑₓₜ = 0), the angular momentum (L) of the system remains constant (L = constant). This principle holds true regardless of the internal forces doing the work.

  9. Q9. The moment of inertia of a circular disc of mass M and radius R about an axis passing through its center is:

    • A1/3MR²
    • B1/2MR²
    • CMR²
    • D1/4MR²
    Show answer & explanation

    Correct answer: B — 1/2MR²

    The moment of inertia (I) of a uniform solid disc rotating about its center is I = 1/2MR².

  10. Q10. The unit of angular momentum is equivalent to the unit of which physical quantity?

    • AJoule
    • BKilogram-meter/second
    • CNewton-meter
    • DWatt
    Show answer & explanation

    Correct answer: B — Kilogram-meter/second

    Angular momentum is calculated as the product of moment of inertia and angular velocity. The standard SI unit is kg⋅m²/s, which is equivalent to J⋅s (Joule-second), making the unit of angular momentum equivalent to the unit of angular impulse.

  11. Q11. A body is rotating with angular velocity ω and has a moment of inertia I. If the angular momentum of the body is L, which of the following quantities is correctly related to L and ω?

    • AL = Iω
    • BL = I²ω
    • CL = I/ω
    • DL = I/ω²
    Show answer & explanation

    Correct answer: A — L = Iω

    Angular momentum (L) is defined as the product of the moment of inertia (I) and the angular velocity (ω). Thus, L = Iω.

  12. Q12. A body rotating about a fixed axis has an angular momentum L. If the moment of inertia of the body is doubled while the angular velocity remains the same, what happens to the angular momentum?

    • AThe angular momentum is halved
    • BThe angular momentum remains unchanged
    • CThe angular momentum is quadrupled
    • DThe angular momentum is doubled
    Show answer & explanation

    Correct answer: D — The angular momentum is doubled

    Angular momentum L is defined as L = Iω. If I is doubled and ω is constant, the new angular momentum L' = (2I)ω= 2(Iω) = 2L.

  13. Q13. Two objects are connected by a light, inextensible string and roll down an inclined plane. If the only external force acting is gravity, what is the relationship between the angular momentum of the system and the linear momentum of the center of mass?

    • ABoth angular momentum and linear momentum are conserved
    • BLinear momentum is conserved, but angular momentum is not
    • COnly angular momentum is conserved
    • DAngular momentum is conserved, but linear momentum is not
    Show answer & explanation

    Correct answer: A — Both angular momentum and linear momentum are conserved

    Since the only external force (gravity) acts through the center of mass (or if we consider the external forces acting on the system), the total angular momentum of the system is conserved, just like linear momentum.

  14. Q14. Which of the following statements is true regarding the conservation of angular momentum?

    • AAngular momentum is conserved only when no external force acts on the system.
    • BAngular momentum is conserved whenever the net external torque acting on the system is zero.
    • CAngular momentum is always conserved regardless of the forces involved.
    • DAngular momentum is conserved only for linear motion.
    Show answer & explanation

    Correct answer: B — Angular momentum is conserved whenever the net external torque acting on the system is zero.

    The principle of conservation of angular momentum states that angular momentum is conserved if and only if the net external torque acting on the system is zero (τₙₑₜ = 0).

  15. Q15. If the net external torque acting on a system is zero, what can be concluded about the angular momentum of the system?

    • AAngular momentum is conserved
    • BAngular momentum is decreasing
    • CAngular momentum is zero
    • DAngular momentum is continuously increasing
    Show answer & explanation

    Correct answer: A — Angular momentum is conserved

    The principle of conservation of angular momentum states that if the net external torque (τₙₑₜ) acting on a system is zero, the angular momentum (L) of the system remains constant (L = constant).

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