Q. We apply a force of 200 Newtons on a wooden Box and push it on the floor at constant velocity. The marginal friction force will be:

Correct Answer: b) 200 Newtons

Explanation:
– The box is moving at constant velocity, which means its acceleration is zero.
– By Newton’s First Law (or using ΣF = m·a), if acceleration is zero, the net force must be zero.
– Along the direction of motion: Applied force − Friction force = 0 ⇒ Friction force = Applied force.
– Therefore, the kinetic (sliding) friction balances the push: Friction = 200 N, opposite to the motion.