1. The coefficients of friction between a block of mass 1.0 kg and a surface are

Question

1. The coefficients of friction between a block of mass 1.0 kg and a surface are ?s = 0.75 and ?k = 0.45. Assume the only other force acting on the block is that due to gravity. What is the magnitude of the frictional force (in newtons) on the block if the block is at rest and the surface is horizontal? Use g = 9.79 m/s^2.

2. The coefficients of friction between a block of mass 2.0 kg and a surface are ?s = 0.60 and ?k = 0.25. Assume the only other force acting on the block is that due to gravity. What is the magnitude of the frictional force (in newtons) on the block if the block is at rest and the surface is inclined at ? = 19°? Use g = 9.79 m/s2.

Explanation / Answer

a) if the block is at rest

=> frictional force =Us*N = Us*m*g = 0.75*1.0*9.79 = 7.34 N

b) if the block is at rest

=> frictional force = Us*N = Us*m*gcos(19 degree) = 0.60*2.0*9.79*0.945 = 11.10 N

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