13. Rotational Inertia & Energy

A hollow sphere of mass $15\mathrm{g}$ and radius of $4.0\mathrm{cm}$ rolls without slipping down a $30\mathrm{cm}$ high ramp angled at 20° above the horizontal. What is the speed of sphere when it reaches the bottom of the ramp? Ignore air resistance.

A 2.20-kg hoop 1.20 m in diameter is rolling to the right without slipping on a horizontal floor at a steady 2.60 rad/s. (c) Find the velocity vector of each of the following points, as viewed by a person at rest on the ground: (i) the highest point on the hoop; (ii) the lowest point on the hoop; (iii) a point on the right side of the hoop, midway between the top and the bottom.