Question about springs and rotational/translational energy

[neel400]

Homework Statement

Hi i need help with this problem ASAP

Relevant Equations

1/2kx^2, mgh, 1/2mv^2, 1/2Iw^2

View attachment 353342
A thin uniform rod has mass M=0.510 kg and length L=0.470 m. It has a pivot at one end and is at rest on a compressed spring as shown in (A). The sequence below shows that the rod is released from an angle θ1=59 degrees, and moves through its horizontal position at (B) and up to (C) where it stops with θ2=111 degrees, and then falls back down. Assume friction at the pivot is negligible.

a) Calculate the (translational) speed of the center of mass (CM) at (B) in m/s.
b) The spring in (A) has a length of 0.1240.124 m and at (B) a length of 0.1540.154 m. Calculate the spring constant k in N/m.

Please help with setting up an equation that can solve for a and b, I'm very lost with what to do.

I originally set it up as A: negative gravitational and elastic energy, B: Kinetic and rotational energy and C: positive gravitational (and tried with and without a rotational energy here), but i got the wrong answer. I'm not sure if it's an error in the way i understood which energies are present and which point, or if there is something wrong in my calculations due to the center of mass (im not very certain how to factor that in -- i used it for the mgh calculations, but not sure if i need to use it elsewhere)

 

[kuruman]

According to our rules, to receive help, you need to show some credible effort towards answering the question. How about telling us what you do know and how you would approach this problem?

Please read, understand and follow our homework guidelines, especially item 4, here
https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/

 

[mfb]

The attachment doesn't work.

I originally set it up as A: negative gravitational and elastic energy, B: Kinetic and rotational energy and C: positive gravitational (and tried with and without a rotational energy here), but i got the wrong answer.

The elastic energy will still be relevant at B and C, unless the object is released from the spring.

It stops at C so there is no kinetic energy left (rotational kinetic energy is kinetic energy, too).

We can't tell what went wrong if you don't show your approach.

 

[Lnewqban]

Welcome, @neel400 !

Is the described set up similar to this one?

 

[kuruman]

Welcome, @neel400 !

Is the described set up similar to this one?

View attachment 353351

That's it. I remember seeing it when I replied to the OP. It then disappeared in a "Black Hole" probably by a mentor's action.