Athlete’s Acceleration and Friction – Rankers Physics

Work Done by Constant and Variable Forces: Practice Problem & Solution

Assertion (A): An athlete accelerates from rest to its maximum speed due to friction between his shoes and track. Reason (R): Positive work done by frictional force increases the kinetic energy of athlete.
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 Work Done by Constant and Variable Forces. Understanding the underlying formula is key to arriving at the correct answer below:

Assertion is true: An athlete pushes backward on the ground, and the ground exerts a forward static friction force on the athlete, causing acceleration.

Reason is true: The static friction force acts in the direction of the athlete's motion. Therefore, it does positive work, which directly increases the athlete's kinetic energy \(K\) according to the work-energy theorem.

Both A and R are true, and R provides the correct explanation for A.

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