Question

In the figure, a horizontal force F is applied such that the block remains stationary. Which of the following statements is false?

• A. (A) f = mg [where f is the friction force]
• B. (B) F = N [where N is the normal force]
• C. (C) F will not produce torque
• D. (D) N will not produce torque

Answer 1

Answer: (D)

(D) N will not produce torque

Answer 2

Explanation:
As the block remains stationary, so for translatory equilibrium,ΣFx=0∴F=Nand ∑Fy=0∴f=mgFor rotational equilibrium, Σt=0 By taking the torque of different forces about point O tF―+tf―+tN→+tmg―=0As F and mg pass through point O ∴cf―+τN―=0As τf―≠0∴τN―∗0, so torques by friction and normal reaction will be in oppositedirections.