A small 700 g ball on the end of a thin, light rod is rotated in a horizontal circle of radius 1.5 m. Calculate the torque needed to keep the ball rotating at a constant angular speed if the air resistance experienced by the ball is 0.1200 N. Ignore the rods moment of inertia and air resistance. Hint: Treat the small ball as a particle.

Question

A small 700 g ball on the end of a thin, light rod is rotated in a horizontal circle of radius 1.5 m.  Calculate the torque needed to keep the ball rotating at a constant angular speed if the air resistance experienced by the ball is 0.1200 N.   Ignore the rods moment of inertia and air resistance.  Hint:  Treat the small ball as a particle.

Damon · Accepted Answer

Torque = .12 * 1.5 Newton meters There is no tangential acceleration so no one cares about the mass.