Question

A rigid body is rotating about an axis. One force F1 acts on the body such that its vector passes through the axis of rotation. Another force F2 acts on it such that it is perpendicular to the axis of rotation and at a point 5cm from the axis. This force F2 is perpendicular to the radius vector at its point of application. Find the net torque on the body. Let F1 = 10N & F2= 5N.

(a) 0

(b) 10.25Nm

(c) 0.25Nm

(d) 10Nm

This question was addressed to me in quiz.

Origin of the question is Dynamics of Rotational Motion about a Fixed Axis topic in division System of Particles and Rotational Motion of Physics – Class 11

Answer 1

Right answer is (c) 0.25Nm

The explanation is: The force F1 passes through the axis of rotation, so it will not produce a torque.

The force F2 is perpendicular to axis and radius, so it will provide a torque = r*F2 about the axis of rotation, where ‘r’ is the distance of point of application of force F2 from the axis of rotation.

Therefore, torque = r* F2= 0.05 * 5 Nm

= 0.25Nm.