An object is kept at rest on a smooth plane inclined at an angle to the horizontal
PHYSICS · Single correct · CBSE · Physics · Laws of Motion · Laws of Motion
Problem
An object is kept at rest on a smooth plane inclined at an angle θ to the horizontal. Which statement best explains why the normal reaction N exerted by the plane is less than the weight mg of the object (for 0<θ<90∘)?
(a) Because the surface is smooth and there is no friction to add to the supporting force, the normal reaction must be smaller than mg.
(b) Upward air resistance on the object supports part of its weight, so the plane needs to exert only a reduced normal reaction.
(c) Only the component of weight perpendicular to the plane ( mgcosθ ) is balanced by the plane, so the normal reaction is less than mg.
(d) The component of weight parallel to the plane ( mgsinθ ) presses the body against the surface; therefore the normal reaction equals mgsinθ(<mg).