Question

A 10-kg block is placed on a horizontal surface. The coefficient of friction between them is 0.2. A horizontal force P = 15 N first acts on it in the eastward direction. Later, in addition to P a second horizontal force Q = 20 N acts on it in the northward direction.

(a) The block will not move when only P acts, but will move when both P and Q act. 

(b) If the block moves, its acceleration will be 0.5 m/s ². 

(c) When the block moves, its direction of motion will be tan ^-1 (4/3) east of north.

(d) When both P and Q act, the direction of the force of friction acting on the block will be tan^-1 (3/4) west of south.

Answer 1

Correct Answer is: (a, b, & d)

Force of limiting friction = F_lim = μmg = 0.2 x 10 x 10 = 20 N.

The block will move when the resultant external force on it exceeds F_lim. When it moves, the direction of the force of friction will be opposite to the block’s direction of motion.