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

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:

Work is \(W = \vec{F} \cdot \vec{d} = Fd cos\theta\). If \(theta = 0\), \(W\) is positive, so (A) is true. Frictional force always opposes motion, so work done by it is negative or zero, never positive. So (R) is true. However, (R) does not explain (A).