A solid uniform-density sphere is tied to a rope and moves (without spinning) in a circle with speed 7 m/s. The distance from the center of the circle to the center of the sphere is 1.8 m, the mass of the sphere is 6 kg, and the radius of the sphere is 0.89 m. The angular speed, w=5.62. What is the rotational kinetic energy of the sphere?

Question

A solid uniform-density sphere is tied to a rope and moves (without spinning) in a circle with speed 7 m/s. The distance from the center of the circle to the center of the sphere is 1.8 m, the mass of the sphere is 6 kg, and the radius of the sphere is 0.89 m. The angular speed, w=5.62.  What is the rotational kinetic energy of the sphere?

anonymous · Answer

I thought I would first need to find Inertia using the formula for spheres (I= (2/5)*M*R^2) and then plug it into the K rotational energy formula, K= (1/2)*I*w^2.  Doing this I got 231.23, but its wrong, the correct answer is 28.7 J.

anonymous · Answer

I think the moment of inertia is just I = m R^2, where m is the mass of the sphere
and R is the 1.8 m from the center of rotation to the center of the sphere.

vincent-lyon.fr · Answer

I'm afraid it is not so clear how the sphere is moving, although the description seems long enough.