Question

A rod is rotating about one end. If a force F1 acting on the other end produces a torque T & supplies power P, find the value of force F2 that will produce the same amount of power when it acts at the midpoint of the rod. Assume that all forces are perpendicular to the axis of rotation & axis of rod. The rod starts from rest.

(a) = F1

(b) > F1

(c) < F1

(d) No force acting at any other point will produce the same power

This question was addressed to me during an interview.

This key question is from Dynamics of Rotational Motion about a Fixed Axis in division System of Particles and Rotational Motion of Physics – Class 11

Answer 1

Correct choice is (b) > F1

For explanation I would say: Power is defined as the work done per unit time. For the same power, the amount of rotation should be the same in a given time. For the th angular acceleration should be the same in both the cases & therefore the torque should be the same.

Thus,  F2* I/2 = F1* I.

F2 = F1*2 OR F2 > F1