Assertion-Reason on System Conservation Laws – Rankers Physics

Angular Momentum and Conservation of Angular Momentum: Practice Problem & Solution

Assertion: In the absence of external torque kinetic energy of a system remains conserved. Reason: In the absence of external torque angular momentum of a system remains conserved.  
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Both Assertion and Reason are true but Reason is not correct explanation of Assertion.
Assertion is true but Reason is false.
Assertion is false and Reason is true.

Solution Explained:

To solve this problem, we apply the core principles of Angular Momentum and Conservation of Angular Momentum. Understanding the underlying formula is key to arriving at the correct answer below:

No external torque means angular momentum is conserved (Reason is true). Kinetic energy may not be conserved as internal forces can change it (Assertion is false).

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Similar Practice Questions

Explore conceptually related problems to test your knowledge.

1. A solid spherical ball rolls on a table. Ratio of its rotational kinetic energy to total kinetic energy is: (1994)
2. Assertion (A): For the purpose of calculation of moment of inertia, body's mass can be assumed to be concentrated at its centre of mass. Reason (R): Moment of inertia of a rigid about an axis passing through its centre of mass is zero.  
3. Assertion (A): By definition, pure rolling of a body occurs when velocity of its point of contact is zero relative to the surface on which it rolls. Reason (R): A body is purely rolling (rolling without slipping). The velocity of point of contact (of body) must be zero with respect to ground.  
4. If moment of inertia of a spinning object drops to \( \left(\frac{1}{4}\right)^{\text{th}} \) of its initial value, the ratio of new rotational kinetic energy to initial rotational kinetic energy will be (Assume net external torque about the axis of rotation is zero)
5. Assertion (A): If earth shrink (without change in mass) to half its present size, length of the day would become 6 hours. Reason (R): As size of the earth changes its moment of inertia changes.