Spring Energy (Finding Velocity)

[Sam Fred]

Homework Statement

A spring AB or constant k = 2N/m is attached to a support A and to a collar of mass
m=1kg. The unstretched length of the spring is 1m, Knowing that the collar is released
from rest at x = x0 = 0.9 m and neglecting friction between the collar and the horizontal
rod, determine the magnitude of the velocity of the collar as it passes through point C.
here l = 1.2m,

Homework Equations

T1 + U1-2 = T2
T Kinetic Energy
U Potential Energy

The Attempt at a Solution

I just wanted to see if the answer is right ??

 

[lewando]

Looks okay.

 

[TSny]

I don't think you handled the work done by the spring correctly. It is not k(.3)²/2.

 

[lewando]

I don't see it... I thought he was correct noting the length of the spring changes from 1.5m to 1.2m.

 

[TSny]

x₂²-x₁² ≠ (x₂-x₁)²

 

[lewando]

Now I see it...thanks.