A common question in physics, which often arises is the question about whether a

Question

A common question in physics, which often arises is the question about whether a friction force, f, does work. If a block is sliding down a rough surface with kinetic coefficient of friction, Mu_k. Carefully reflect on discussions held in class, and then, pick the correct statement about whether the force of friction actually does work on the block, as the block slides down the plane. Select one: a. Work done by friction is equal to zero. b. Work done by friction is greater than zero. c. Work done by friction is less than zero. d. D

Explanation / Answer

Option(c) Work done by the friction is less than zero, is the correct answer.

Explanation -

Frictional force, F = Mu_k*m*g

In moving the block through a distance d, work done by the frictional force -

W = F *(- d) = - Mu_k*m*g*d

Here negative sign is taken for the displacement because force is acting opposite to the displacement of the block.

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