- #1

etothey1

- 8

- 0

## Homework Statement

A spherical billiard ball radius a and mass M is sitting on a flat surface. The coefficient of friction between the ball and table is u. The moment of inertia for the billiard ball is

2Ma^2/5. The ball is given a sharp horizontal hit at the centre and it starts moving with linear velocity Vo. and angular velocity wo=0. Vo is positive.

a, Which way is the point of contact moving? is it rolling or slipping?

b, Draw a diagram showing the forces, to they increase or decrease linear velocity? increase or decrease angular velocity?

## Homework Equations

Friction force = u*m*g

Parallel axis theorem, I= Icm + ml^2 (l is distance from centre)

Newtons second law, F=ma

Torque=rXF=dL/dt, F is force L is angular momentum.

## The Attempt at a Solution

a, point of contact moving leftwards (if ball is rolling to the right), ball is rolling.

b, Friction decreases linear velocity and increases angular velocity.

(However i believe there is an error in the question, regarding the wo=0 part. The angular frequency and linear velocity should decrease linearly together to 0. Therefore if angular velocity is 0 at t=0 then it immedietly spikes up and starts decreasing afterwards.

Anyway, here is my attempt at the solution, however i believe the error lies in the question which is that wo=0 and that it does not ask for the acceleration at a specific point of the ball, which would change the solution.

Any help appreciated!

http://imageshack.us/f/163/lastquestion.jpg

http://imageshack.us/photo/my-images/155/lastquestion2.jpg

http://imageshack.us/f/163/lastquestion.jpg

http://imageshack.us/f/155/lastquestion2.jpg/

Last edited: