# Pebble dropped on rotating wheel, starts to slide after rotation

1. Oct 1, 2013

### zibs.shirsh

1. The problem statement, all variables and given/known data
A wheel of radius R=50cm rolls along the ground with velocity V=2m/s. A pebble released on top of the wheel so that it is instantaneously at rest on the wheel. The co-efficient of friction between wheel and pebble is μ=1. The pebble starts to slide down when it has rotated through angle θ with the vertical axis.

Calculate θ.

2. Relevant equations
Absolutely No idea

3. The attempt at a solution
Couldn't attempt

Last edited: Oct 1, 2013
2. Oct 1, 2013

### Bryson

Try drawing a force diagram. This always helps. I am sure you can think of some relevant equations.

3. Oct 1, 2013

### haruspex

I assume it means at rest relative to the point on the wheel where it is placed.
When the wheel has moved through an angle theta (with the pebble not having slipped yet):
- what point is the pebble rotating about?
- how fast is it moving?
- what force is required to keep it rotating about that point?
- what forces act on the pebble, and in what directions?

4. Oct 1, 2013

### haruspex

I assume it means at rest relative to the point on the wheel where it is placed.
When the wheel has moved through an angle theta (with the pebble not having slipped yet):
- what point is the pebble rotating about?
- how fast is it moving?
- what force is required to keep it rotating about that point?
- what forces act on the pebble, and in what directions?