Assertion and Reason on Kinetic Friction – Rankers Physics

Friction: Practice Problem & Solution

Assertion (A): A body is lying at rest on a rough horizontal surface. A person accelerating with acceleration \(a\) (where \(a\) is positive constant and \(\hat{i}\) is a unit vector in horizontal direction) observes the body. With respect to him, the block experiences a kinetic friction. Reason (R): There is relative motion between the block and surface in person's frame of reference.  
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

Solution Explained:

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

In the accelerating person's non-inertial frame, a pseudo-force acts on the block. If this pseudo-force causes relative motion, kinetic friction acts. A is true. Kinetic friction by definition arises due to relative motion between surfaces. So, R is true and correctly explains A.

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