Friction

Easyphysics

A block of mass 5 kg is placed on a rough horizontal surface. The coefficient of static friction is 0.4. What is the maximum static friction force? (g = 10 m/s²)

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20 N

15 N

25 N

10 N

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Subject: physics
Chapter: laws of motion
Topic: friction
Difficulty: Easy
Year: 2025

Solution

Correct Answer:

20 N

Limiting Friction Definition: The maximum force of static friction that can be exerted between two surfaces is $f_{L} = μ_{s} N$ .
Normal Force ( $N$ ): For a horizontal surface, $N$ is equal and opposite to weight.
- $N = m g = 5 \times 10 = 50$ N.
Subsitution:
- $f_{L} = 0.4 \times 50$ .
Result: $f_{L} = 20$ N.
Note: Static friction is self-adjusting. If you push with 10 N, friction is 10 N. Only when you exceed 20 N will the block move.

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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Friction

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