Am I not supposed to find acceleration from the tangential force?

Question

I keep using the equation a = F/m to find acceleration and then incorporating that into the kinematic equations for constant rotational acceleration. 

 

A(n) 25.0-kg solid sphere of radius 1.20 m is being rotated by applying a constant tangential force of 10.0 N at a perpendicular distance of 1.20 m from the rotation axis through the center of the sphere. If the sphere is initially at rest, how many revolutions must the sphere go through while this force is applied before it reaches an angular speed of 31.0 rad/s?

Answer 1

Instead of using F=ma, use T=I*α (Torque=moment of Inertia*angular acceleration). Since you are looking for a rotational velocity you need to use a rotational acceleration.

 

Also in this case you can't really use F=ma because it relates to linear motion, i.e. the whole mass is not moving at the same acceleration (or velocity). Remember that the center is not moving and the farther from the center the faster it moves.