# Homework Help: Energy question

1. Nov 11, 2008

### asi123

1. The problem statement, all variables and given/known data

Hey guys.
So I got this disk connected to a spring which is connected to a wall.
A mass m hits the disk with a velocity v and sticks to it.
The question is to find the velocity of m at point A.
As you can see I used the conservation of the angular momentum to find $$\omega$$ at the beginning.
The thing I'm not sure about is the energy conservation equation I wrote there, I'm not sure about the gravitational potential energy, I mean, is this right?

10x.

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### scan0011.jpg
File size:
35.3 KB
Views:
73
2. Nov 11, 2008

### asi123

Any idea guys?

3. Nov 11, 2008

### OmCheeto

I'm not sure I fully understand the diagram, but shouldn't v*cos(squiggle)=0?

4. Nov 11, 2008

### asi123

Why?

5. Nov 11, 2008

### OmCheeto

That's why I posted that I didn't understand the diagram.
Is the disk resting on the floor at y=0?
Is the disk pivoted frictionlessly at it's center?

I assumed that since you mentioned gravity, that the disk is in a vertical plane.

My assumption was that the disc was fixed on some axis or point and therefore the v*cos(squiggle) component had to be zero. Also, none of the momentum of the mass m would be imparted to the disc as there was no mention of it's mass. So the magnitude of of the velocity of mass m would have to be the same in the direction of sin(squiggle).

Hope that helps.