Learning Goal: To understand kinetic and static friction. A block of mass M lies

Question

Learning Goal: To understand kinetic and static friction.

A block of mass M lies on a horizontal table. The coefficient of static friction between the block and the table is us. The coefficient of kinetic friction is uk, with uk<us .
A.If the block is at rest (and the only forces acting on the block are the force due to gravity and the normal force from the table), what is the magnitude of the force due to friction?

Part B
Suppose you want to move the block, but you want to push it with the least force possible to get it moving. With what force F must you be pushing the block just before the block begins to move?
Express the magnitude of in terms of some or all the variables f,us ,uk, and m, as well as g the acceleration due to gravity .

Explanation / Answer

Part -A : When the block is at rest there is no frictional force acts on it . so the magnitude of the force due to friction is zero. Part -B : When the block is just ready to move , then the frictional force comes in the action and opposes the motion of the block . So in order to move the block by overcoming the force the friction , the magnitude of minimum force required is F = usMg

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