Answer to Question #270461 in Physics for Jane

Question

1. 200-gram ball, m1 and a 100-gram ball, m2, connected by a rod with length of 60 cm. The axis of rotation is located at ball m2. What is the moment of inertia of the balls. Ignore rod’s mass
2. A slim rod 2.0 m long has two small 0.50-kg bodies attached at its two ends and a 0.25-kg body at its midpoint as shown. Find the moment of inertia about an axis perpendicular to the rod has negligible mass.
3. Four identical masses of 2.0 kg each situated at the four corners of a square. A side of the square measures 3.0 m. Find the moment of inertia about an axis passing through the center of the square and perpendicular to its plane. 

Answer 1

1. $I=0.2\cdot0.6^2=0.072\ (kg\cdot m^2)$

2. $I=0.5\cdot0.5^2+0.25\cdot(1-0.5)^2+0.5\cdot(1+0.5)^2=$

$=1.3125\ (kg\cdot m^2)$

3. $I=4\cdot2\cdot(\sqrt{18}/2)^2=36\ (kg\cdot m^2)$