Friction in Pure Rolling – Rankers Physics

Rolling: Practice Problem & Solution

Assertion (A): When the disc rolls without slipping, friction is required because condition of pure rolling is velocity of point of contact is zero. Reason (R): The force of friction in the case of a disc rolling without slipping down an inclined plane is zero.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Short Solution (Best for NEET):

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

Assertion (A) is true: For pure rolling, the point of contact velocity is zero, and friction provides the necessary torque.

Reason (R) is false: For a disc rolling without slipping down an inclined plane, friction is present and acts up the incline to provide the torque for rotation. Thus, (A) is true, (R) is false.

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