# Homework Help: Conservation of energy with springs and rotational motion

1. Nov 14, 2012

### theBEAST

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

2. Relevant equations
T1 + V1 = T2 + V2

T = kinetic energy
V = potential energy

3. The attempt at a solution
I am only confused about how to get T2. Here is how the answer key gets T2:

I don't get why Va = Vb = 0. The wheels have some velocity so it doesn't make sense how they are zero. I realize that they won't rotate because there is no friction but I still think there is a velocity.

I also don't get why they can assume that the rods are pinned. How are they pinned when the spring stretches from √2 to 2m in length (this is from the solution as well)?

2. Nov 14, 2012

### lewando

Va=Vb=0 only when θ = 0. At this angle, AC and CB are horizontal and the maximum separation between A and B has been achieved.

''pinned" is not an assumption, it is expressly given--"All pin joints move without friction". Not sure what the answer key means by like "pinned case".

Last edited: Nov 14, 2012