# Homework Help: Angular impulse of rolling ball

1. Nov 3, 2012

### serverxeon

In the following, we have a sliding sphere, when it meets a floor with friction.

I want to use the angular impulse method to find an expression of the v when pure rolling starts.

[sorry I have no idea how to type in latex.]

This is obviously incorrect.
But I cant find out what's wrong. anyone?

2. Nov 3, 2012

### xur54

Why is that obviously wrong? I at least could follow it. (Small note: you changed from r to R in the problem. Also I think Vi should equal Vi not Vi=V because if Vi=V that's like Vi=Vf, but that's more of a typo.)

Last edited: Nov 3, 2012
3. Nov 3, 2012

### serverxeon

it's wrong cos it states that mv is larger tahn the impulse given.

4. Nov 3, 2012

### xur54

?? Kind of following. Why does that matter? The value of mv can be bigger than the linear impulse in this problem. (Note: where mv=mVfinal)

5. Nov 3, 2012

### haruspex

It might become clearer if you properly distinguish initial and final linear speeds (u, v perhaps) and get the relationship between them.