# Week 13 (Nov. 4 - 8)

Reading: PSE Chap 10, Rotation of a rigid body about a fixed axis
Topics: angular velocity, angular acceleration, rotational kinematics

Lab:

Homework Problems: Due Tuesday , Nov. 14 at noon.

1. Rotating record player problem: Consider a record player. The record, in the form of a disk, spins at a rate of 33 revolutions per minute. A small bug of mass m = 1 gram is located 10 cm from the axle; it clings tenaciously to the record as it spins.
• What is the period of revolution, T, of the record, in seconds.
• What is the frequency of revolutions, f, in Hz.
• What is the angular speed, omega, in radians per second.
• If, at time t = 0, the bug is located at an angle theta = 0, then through what angle has the bug moved in one second? Report this in both radians and in degrees.
• Is the bug accelerating as it clings to the record player? If so, then what is the magnitude and direction of the acceleration?
2. Slowing record player problem: Suppose now that the record player to which the bug is clinging, which is initially turning at 33 rpm, is turned off. It decelerates at a constant rate until it comes to a stop 10 seconds later.
• What is the angular deceleration, alpha, of the record player (in radians per second squared)?
• Make a plot of the angular speed as a function of time. Appropriately label your plot.
• What is the angular speed, omega (in radians per second), of the record player at t = 5 seconds?
• What is the speed of the bug at this moment in time?
• What is the acceleration of the bug at this moment in time? In particular, what are the magnitude and directions of both the centripetal and tangential acceleration of the bug at this moment?
• What is the magnitude of the frictional force acting on the bug at this moment?

Quiz: Monday, Nov. 6. Covering conservation of energy and momentum.
General College Physics