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

## Homework Statement

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.

## Homework Equations

Absolutely No idea

## The Attempt at a Solution

Couldn't attempt

Last edited:

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

haruspex
Homework Helper
Gold Member
2020 Award
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?

haruspex
Homework Helper
Gold Member
2020 Award
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?