Question

A small block of mass of 0.1 kg lies on a fixed inclined plane PQ which makes an angle q with the horizontal. A horizontal force of 1 N acts on the block through its center of mass as shown in the figure. The block remains stationary if (take g = 10 m/s²)

(A) θ = 45° 

(B) θ > 45° and a frictional force acts on the block towards P. 

(C) θ > 45° and a frictional force acts on the block towards Q. 

(D) θ < 45° and a frictional force acts on the block towards Q

Answer 1

Correct options are (A) and (C)

If θ = 45º then cos θ = sin θ hence block will be at rest.

If plane is rough & θ > 45° then sin θ > cos θ so friction will act up the plane.

If plane is rough & θ < 45 then cos θ > sin so friction will act down the plane so (A, C) are correct.

Answer 2

Correct answer is

(A) θ = 45°

(C) θ > 45° and a frictional force acts on the block towards Q.