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 b…

Question

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:

1. A. 100 Newtons
2. B. 200 Newtons (Correct answer)
3. C. 300 Newtons
4. D. 400 Newtons

Correct Answer

Option B — 200 Newtons

Detailed Solution & Explanation

The correct answer is 200 Newtons.

Key Points

• The key phrase in the question is "constant velocity".
• When a body moves at constant velocity, its acceleration is zero, and by Newton's Second Law (F = ma) the net force acting on it must also be zero.
• Since the applied force of 200 N pushes the box forward and the only opposing horizontal force is kinetic friction, these two must be equal and opposite for the net force to vanish.
• Therefore the limiting (marginal) friction force is exactly 200 N.
• This is a direct application of Newton's First Law (the law of inertia): a body continues in uniform motion unless acted upon by an unbalanced external force.
• Note that friction acts opposite to the direction of relative motion, and that kinetic friction is independent of the area of contact and of speed.

Exam Tip

• whenever a question says "constant velocity", "uniform speed" or "equilibrium", immediately write net force = 0 — that single step solves most such numericals.

प्रश्न (हिन्दी में)

हम एक लकड़ी के बक्से को 200 न्यूटन बल लगाकर उसे नियत वेग से फर्श पर ढकेलते हैं। सीमान्त घर्षण बल होगा:

1. A. 100 न्यूटन
2. B. 200 न्यूटन
3. C. 300 न्यूटन
4. D. 400 न्यूटन