friction

Question

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)

RankGuru · Accepted Answer

1. **Limiting Friction Definition**: The maximum force of static friction that can be exerted between two surfaces is $f_{L} = \mu_s N$.
2. **Normal Force ($N$)**: For a horizontal surface, $N$ is equal and opposite to weight.
   - $N = mg = 5 	imes 10 = 50$ N.
3. **Subsitution**:
   - $f_L = 0.4 	imes 50$.
4. **Result**: $f_L = 20$ N.
5. **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.

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