A block of mass m is on an inclined plane of angle `theta`. The coefficient of friction between the block and the plane is `mu` and `tanthetagtmu`. The block is held stationary by applying a force P parallel to the plane. The direction of force pointing up the plane is taken to be positive. As P is varied from `P_1=mg(sintheta-mucostheta)` to `P_2=mg(sintheta+mucostheta)`, the frictional force f versus P graph will look like

Options

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Answer

A

Explanation

Given that tan `theta gt mu` it means the block will slide downward and force of friction will act up the plane , i.e., positive . The instant at which applied force P is equal to mg sin `theta` , tendency of the block to slide down the inclined plane will cease and frictional force vanishes . As P is further increased , the block will move up the inclined plane and hence friction will act down the plane , i.e., negative .