# Calculating the mass of the wheel on a pendulum on a watch

1. May 4, 2013

### NathanLeduc1

1. The problem statement, all variables and given/known data
The balance wheel of a watch is a thin ring of radius 0.95 cm and oscillates with a frequency of 3.10 Hz. If a torque of 1.1x10-5 Nm causes the wheel to rotate 45°, calculate the mass of the balance wheel.

2. Relevant equations
I=mr2
T=(2π)sqrt(I/mgh)
τ=-Kθ

3. The attempt at a solution
I got an answer but it's wrong...

Here's the work I did:
1.1e-5=-K(pi/2)
K=-7.003e-6
380.25 rad/s2 = 7.003e-6 Nm / 9.025e-5m M
M*0.0343 m/s2 = 7.003e-6 Nm
m = 2.04e-4 kg

(I realized just now that I took the square root of a negative number earlier. I tried to redo the problem but I'm still stuck...) Thanks!

2. May 4, 2013

### SammyS

Staff Emeritus
Is that the complete problem, word for word.

It seems that some information is missing. I could guess at what's missing, but it would be just a guess.

3. May 4, 2013

### NathanLeduc1

Yep, that's the question word for word.

4. May 4, 2013

5. May 4, 2013

pi/4

6. May 4, 2013

### NathanLeduc1

Oh my goodness... I just realized why you were asking me that. Wow, I am dumb. Man, those stupid mistakes get me every time. Thanks for the help.