Unstretched Spring and Angular Velocity Problem

[BitterSuites]

[SOLVED] Unstretched Spring and Angular Velocity Problem

Homework Statement

A disk of mass 73 kg is held by a spring of unstretched length 88 cm and stiffness constant 430 N/cm, and rests on a frictionless table. It is then orbited in a circle at angular velocity .675 rad/s.

By how much is the spring stretched? Answer in units of cm.

Homework Equations

After a bit of derivation, I came up with x = r/((k/mw^2)-1).

The Attempt at a Solution

r = 88
k = 430
m= 73
w = .675

It does not seem to work out. Am I being to complicated about it? Any help/hand-holding is greatly appreciated.

 

[physixguru]

Force acting on the disc in circular motion== mv^2/r

Now use hook's law to calculate extension..

 

[Doc Al]

After a bit of derivation, I came up with x = r/((k/mw^2)-1).

Looks good to me.

The Attempt at a Solution

r = 88
k = 430
m= 73
w = .675

Make sure you are using standard units. Express lengths (and k) in terms of meters, not cm.

 

[BitterSuites]

Thanks for the catch on conversion. I changed length to .88 and K to 4.3, getting an answer in m. I then converted it to cm but the online system still says I am incorrect.

I can't use mv^2/r because I don't have v. That is why I did that insane derivation.

Or am I wrong?

I think I'm a few baby steps away from having this.

 

[Doc Al]

I changed length to .88 and K to 4.3...

Redo that last one.

 

[BitterSuites]

Uh oh. Did I go the wrong way with it? 43000N/m?

 

[Doc Al]

That's better.

 

[BitterSuites]

Oh, thank you so much *sighs in relief*

Converting correctly makes the problem work. Who knew? :D