A block of mass m is placed on a smooth inclined plane of inclination θ with the horizontal. The force exerted by the plane on the block has a magnitude

From the free-body diagram,



The force exerted by the mass m on the plane is.


Since the action and reaction are equal and opposite, the force exerted by the plane on the block will be in a direction opposite to the normal component of the force exerted by the block on the plane.
Therefore, N = mg cosθ
Normal force exerted by the plane on the block is mg cosθ.

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