Free body diagram of atwood machine

[Shukie]

Homework Statement

I need to find the forces on this modified atwood machine:

http://imageshack.us/photo/my-images/36/atwood.jpg/

The Attempt at a Solution

What I think:

- On mass M there are two forces, Mg and -T.
- On the mass above the spring there are two more forces, -2mg and T.
- On the mass below the spring there are also two forces, -mg and kx.

Is any of this correct?

 

[soothsayer]

You seem to have got it right.

 

[Shukie]

Thanks.

 

[Doc Al]

- On the mass above the spring there are two more forces, -2mg and T.

Careful: The only force of gravity on that mass is mg. (But there's a spring force on it.) So there are three forces acting on that mass.

 

[soothsayer]

Careful: The only force of gravity on that mass is mg. (But there's a spring force on it.) So there are three forces acting on that mass.

Ooh, you're right, I was thinking there might be a 2mg plus a kx after you mentioned the spring force, but I think it's only mg and kx.

I knew the spring was going to make it trickier than I had thought.

 

[Shukie]

Are the forces on the mass above the spring then T and -mg and - kx?

 

[Doc Al]

Are the forces on the mass above the spring then T and -mg and - kx?

Yes.

 

[Shukie]

Thanks