Question

A 2.0 kg ball and a 3.5 kg ball are connected by a 2.0 m long rigid, massless rod. The rod and balls are rotating clockwise about its center of gravity at 21 rpm .

What torque will bring the balls to a halt in 6.0s?

Answer 1

21 rpm = 2.20 rad/s

Angular deceleration rate required
= alpha = 2.2/6.0 = 0.367 rad/s^2

Torque required = I*alpha

where I is the moment of inertia. I will leave you to calculate that. First you need to locate the center of mass and the distances of the masses from that center.

Answer 2

13