posted by Erin on .
A thin, light string is wrapped around the rim of a 4.00kg solid uniform disk that is 30.0cm in diameter. A person pulls on the string with a constant force of 100N tangent to the disk. Find the linear acceleration of its center of mass. If the disk is replaced by a hollow thin-walled cylinder of the same mass and diameter, what will be the angular acceleration of the disk about its center of mass and what will be the linear acceleration of its center of mass?
Since the pulled string exerts the only force on the disc (assuming that gravity is ignored here), you can use
F = m a for the acceleration of the center of mass, in both cases.
Pulling the string also starts the disk spinning at an acclerating spin rate. Use the relation
Torque = Force * R = I* alpha
for the angular rate of acceleration, alpha. I, the moment of inertia, will be different for the solid disc and the thin walled disc, despite the equal masses.