Question

39. A block of mass m is at rest under the action of force F against a wall as shown in figure. Which of the following statemet is incorrect ? (1) f = mg (where f is the frictional force) (2) F N (where N is the normal force) (3) F will not produce torque (4) N will not produce torque he pulleys and strings shown in the figure are smooth and of negligible mass. For the system to

answer is 4.pls explain well.

Answer 1

Torque is produced when a force is applied perpendicular to a lever , which force the lever to rotate about an axis. so torque is the cross product of perpendicular force and distance from the axis about which the lever rotates$torque = F \times d = |F||d| sin\Theta$

here the angle between Normal force and distance is zero. so $sin\Theta = sin0 = 0$

so normal N will not produce any torque.