In a situation the contact force by a rough horizontal surface on a body placed on it has constant magnitude. If the angle between this force and the vertical is decreased, the frictional force between the surface and the body will
Let us assume that the force F is applied on the body making an angle θ with the vertical. By resolving the component of force F, the horizontal component Fsinθ is equal to the frictional force. So, as the value of θ decreases, frictional force also decreases. It is already given that force F is constant, so frictional force will decrease.
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