A hoop $($I$=$MR$2)$ and a solid cylinder $($I$=(1)/(2)$ MR$2)$ have the same mass M and the same radius R$.$ They roll down an inclined plane $($without slipping$)$ from the same height. a$)$ Which arrives at the bottom with the greater speed? b$)$ Which arrives with the greater angular momentum about its axis? Explain your answers