# Week 14 (Nov. 11 - 15)

**Reading:**PSE Chap 11, Rolling motion, angular momentum and torque

**Topics:**torque, rotational dynamics.

**Quiz on Monday this week**

**Week 14 Homework Problems:**

**Rotational inertia of triangle:**Three 1 kg masses are fixed at the corners of an equilateral triangle. The sides have length 2 meters. If this triangular system rotates around the center of mass of the triangle, then what is its rotational inertia?**Automobile problem:**A 1500 kg automobile has a wheel base (distance between wheels) of 3 meters. The center of mass of the automobile is on at the center line at a point 1.2 meters behind the front axle. Find the force exerted by the ground on each wheel.**One mass suspended from pulley:**A 10 kg mass is suspended from a thin string. The string is wrapped a bunch of times around a solid disk that acts as a pulley. The disk/pulley has a mass of 2 kg and a diameter of 5 cm. The mass is released from rest and so it begins to descend due to its weight. As it does so, the string, which is wrapped around the disk, causes the disk to rotate (the string does not slip).- How much torque does the 10 kg mass exert on the disk?
- What is the angular acceleration of the pulley as the 10 kg mass falls? Is it constant?
- What is the angular velocity of the pulley? Is it constant, or time dependent?
- The floor is 3 meters beneath the release point of the 10 kg mass. How long does it take to hit the floor?
- What is the speed of the mass just before it hits the floor?