South Pasadena Physics Name

South Pasadena • Physics Name 8 · Rotational Mechanics Period Date 8 . 2 Q U I C K C H E C K Solid Cylinder I = ½ mr2 Hoop or Ring I = mr2 Solid Sphere I = 2/5 mr2 L=I x Review Problems. Try these problems. Use  or  to indicate whether you’re confident about it. 1. Two masses of 3.1 kg and 4.6 kg are attached to either end of a thin, light rod (assume massless) of length 1.8 m. Compute the moment of inertia for:     a) The rod is rotated about its midpoint. b) The rod is rotated at a point 0.30 m from the 3.1 kg mass. Work: Notes:

2. You spin a ball of mass 0.18 kg that is attached to a string of length 0.98 m     at ω = 5.2 rev/s in a circle. What is the ball’s angular momentum? Work: Notes:

3. A skater has a moment of inertia of 100 kg m2 with his arms outstretched and a moment of inertia of 75 kg m2 when his arms are tucked close to his     body. If he starts his spin with an angular speed of 2 rev/s and his arms outstretched, what will his angular speed be when he brings them in? Work: Notes:

4. Calculate the angular momentum of a ballet dancer who is spinning at 1.5 rev/sec. Model the dancer as a cylinder (I = ½ MR2) with a mass of 62 kg, a     height of 1.6 m and a radius of 0.16 m. Work: Notes: 5. A small 1.05-kg ball on the end of a light rod is rotated in a horizontal circle of radius 0.900 m. Calculate a) the moment of inertia of the system about the axis of rotation,     b) the torque needed to keep the ball rotating at constant angular velocity if air resistance exerts a force of 0.0800 N on the ball. Work: Notes: