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Homework 8
Chapter 10: 22, 34, 41, 42, 51, 57, 69
Additional Problems:
1. Calculate the rotational inertia of a meter stick, with mass 0.70 kg, about an axis
perpendicular to the stick and located at the 19 cm mark. (Treat the stick as a thin rod.)
Ans. 0.126 kg·m2
2. Figure (a) shows a disk that can rotate about an axis at a radial distance h from the
center of the disk. Figure (b) gives the rotational inertia I of the disk about the axis as a
function of that distance h, from the center out to the edge of the disk. The scale on the I
axis is set by IA = 0.030 kg·m2 and IB = 0.630 kg·m2. What is the mass of the disk?
Ans. 15 kg

3. A thin rod of length 0.75 m and mass 0.35 kg is suspended freely from one end. It is
pulled to one side and then allowed to swing like a pendulum, passing through its lowest
position with angular speed 3.7 rad/s. Neglect friction and air resistance.
(a) Find the rod's kinetic energy at its lowest position
Ans. 0.449 J
(b) Find how far above that position the center of mass rises.
Ans. 0.131 m
4. A small ball of mass 0.85 kg is attached to one end of a 1.05 m long massless rod, and
the other end of the rod is hung from a pivot. When the resulting pendulum is 35° from
the vertical, what is the magnitude of the torque about the pivot?
Ans. 5.02 N·m