21) A uniform hollow spherical ball of mass 1.75 kg and radius 40.0 cm rolls without slipping up a ramp that rises at 30.0 above the horizontal. The speed of the ball at the base of the ramp is 2.63 m/s. While the ball is moving up the ramp, find (a) the acceleration (magnitude and direction) of its center of mass and (b) the friction force (magnitude and direction ) acting on it duc to the surface of the ramp. 9.33 * A wagon wheel is con- Figure E9.33 structed as shown in Fig. E9.33. The radius of the wheel is 0.300 m. and the rim has mass 1.40 kg. Each of the eight spokes that lie along a diameter and are 0.300 m long has mass 0.280 kg. What is the moment of inertia of the wheel about an axis through its center and perpen- dicular to the plane of the wheel? (Use Table 9.2.) 0.600 m