Question

Of the following objects, which would rotate the fastest (maximum angular acceleration) if the same force is applied to each (10.0 N). Mark a number 1 for highest, 4 for lowest, etc. Assume a 1 kg mass for each.

A Hollow sphere (radius 0.50 m)

A solid sphere (radius 0.50 m)

A rod rotating about its center (radius is 0.50 m, length is 1.00 m)

A rod rotating about its edge (length 0.50 m).

Answer 1

denotes Moment of inertia

         

         

Clearly Moment of inertia of rod about its edge is maximum and that of the rod about C.M is minimum. Therefore rod will rotate fastest about its center of mass, and rod about edge will rotate slowest.

1   Rod rotating about Its C.M. (Maximum)

4   Rod rotating about Its edge. (Minimum)