# Stability of a teeter-toy-classical mechanics

1. Jan 7, 2016

### Saph

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

In the image above, the toy consists of two identical mass hanging from a peg. we take the zero potential energy at the pivot.

2. Relevant equations:
http://www.physicsmynd.com/?p=1172

3. The attempt at a solution
Since the potential energy is zero at the pivot, and the potential energy is defined by U(θ)=mgh, I had:
U(θ)= mg(- l*cos(α+θ)- l*cos(α-θ))
but the solution is: U(θ)= mg(L*cos(θ) - l*cos(α+θ)) +mg(L*cos(θ) - l*cos(α-θ))

So my question is,what is wrong with my answer, and why?

2. Jan 7, 2016

### TSny

The zero of PE is at the pivot point.
l*cos(α-θ) is not the vertical distance between the pivot point and the mass on the right.

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3. Jan 9, 2016

### Saph

Thank you very much sir, I think my problem was with English more than it was with physics, I thought what he meant be pivot is the joining point of the arms with the peg, now I got the solution right.

4. Jan 9, 2016

### TSny

OK. Good.

5. Oct 14, 2016

### ERK1

Hello, could you please publish or send to me the correct solution to that example?

6. Oct 14, 2016

### ERK1

Hello, could you please publish or send to me the correct solution to that example?

7. Oct 15, 2016

### haruspex

That's not how things are done here. If you have been given the same homework task and need help, please post your own attempt; maybe in a new thread.

8. Oct 18, 2016

### Bambisu

Can someone do all my physics homeworks please and post them to me on time and not a minute late ?