Force to Start a Block Sliding
Easyfriction
A 50 kg block rests on a horizontal surface with coefficient of static friction μs = 0.30. What horizontal force is required to start it moving? Use g = 9.81 m/s2.
- A147 N
- B490 N
- C15 N
- D50 N
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Answer: A. 147 N
On a level surface the normal force equals the weight: N = m g = 50 · 9.81 = 490.5 N. Impending motion means F = μs · N = 0.30 · 490.5 = 147 N. 490 N is the weight itself; 15 N mistakes mass for weight.
N N
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