Angular impulse of rolling ball

[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 can't find out what's wrong. anyone?

 

[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.)

 

[serverxeon]

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

 

[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)

 

[haruspex]

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