# Finding torsion constant of the wire?

## Homework Statement

A torsional pendulum consists of a disk of mass 450 g and radius 3.5 cm, hanging from a wire. If the disk is rotated through an angle of 45o and released from rest and oscillates with a frequency of 2.5 Hz, what is the torsion constant of the wire?
• A :

• B :

• C :

• D :

• E :

## Homework Equations

Torque = -k(torsion constant) * theta
Torque = r * F*sin theta

## The Attempt at a Solution

So i had to google "torsion constant equation" because i couldn't find an equation in my book so im hoping this is the right equation. Then i used the second torque equation to find torque. I did T = .035m * (.45kg * 9.8(gravity))*sin(45) = .10914.

Then i plugged the answer for T into the first equation T = -k *theta. So .10914 = -k * (pi/4), i converted 45 degrees to pi/4 radians. Then I divided .10914/(pi/4) = .13896.

So my overall answer was .13896. This is not one the options above so i know I did not do something correctly. I'm almost positive its from not having the right equations for the questions.

Advice would be great, thanks everyone! 