# Homework Help: Dynamics question

1. Mar 16, 2009

### sArGe99

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

Find out the acceleration of the rod A and the wedge B in the arrangement if the ratio of mass of the wedge to that of the rod equals $$\eta$$, and the friction between all contact surfaces is negligible

2. Relevant equations
Mass of rod = m, Mass of wedge = M

mg - $$N cos \alpha$$ = ma, downwards

3. The attempt at a solution
Normal reaction is perpendicular the wedge surface and I don't know if it has a component that can accelerate the wedge to the right. If the force is moving to the left, surely the wedge can't be accelerated to the left.

I need to know which force accelerates the wedge to the right. I'm thinking that the normal reaction has the component $$N sin \alpha$$ directed to the left.
If I knew which component of force was directed to the right, I could solve the remaining part of it.

Last edited: Mar 16, 2009
2. Mar 16, 2009

### sArGe99

3. Mar 16, 2009

### tiny-tim

Welcome to PF!

Hi sArGe99! Welcome to PF!

conservation of energy?

4. Mar 16, 2009

### sArGe99

Yes. I did try that out. Don't think I have got enough information to use that.

5. Mar 16, 2009

### sArGe99

Normal reaction acts perpendicular to the wedge surface. Is that right, in this case?
I think that is where I might have gone wrong.

6. Mar 16, 2009

### tiny-tim

Yes you have …

try again (use x and x', where x is horizontal displacement), and show us what you get

7. Mar 16, 2009

### sArGe99

I think the kinematic relationship is Distance moved by Rod / Distance moved by wedge = tan (alpha)?

8. Mar 17, 2009

### tiny-tim

just woke up :zzz: …
You know it is …

get on with it!

9. Mar 17, 2009

### sArGe99

Oh.. I could do with this one, I guess.
It can be solved using force equations, right? I actually wanted to try that method out first.