Friction
A wooden block resting on a rough horizontal floor just begins to slide when a horizontal pull equal to 24 N is applied, while the block weighs 60 N. What is the coefficient of static friction between the block and the floor?
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About This Question
- Subject
- physics
- Chapter
- laws of motion
- Topic
- friction
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
0.4
From NCERT Class 11, Chapter 5 (Laws of Motion), the limiting (maximum) static friction is given by f_max = μ_s N, where N is the normal reaction. On a horizontal floor with only weight acting vertically, the normal reaction equals the weight, so N = 60 N. The block is on the verge of sliding when the applied horizontal force equals the limiting static friction, so f_max = 24 N. Rearranging, μ_s = f_max / N = 24 / 60 = 0.4. Option 0.6 incorrectly inverts the ratio as 60/24 scaled, or confuses force with weight. Option 0.25 corresponds to taking 24/96, using a wrong normal force. Option 0.5 corresponds to 30/60 and does not match the given applied force. Plausibility check: coefficients of static friction for wood on a typical floor lie around 0.3 to 0.5, so 0.4 is physically realistic, and being dimensionless it correctly carries no units, confirming the result.
This easy difficulty physics question is from the chapter laws of motion, covering the topic of friction. It appeared in the 2025 exam.
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