# Homework Help: Harmonic Motion Problem

1. Jan 25, 2010

### MorganJ

1. The problem statement, all variables and given/known data
-A pendulum with a length of 1.00 m is released from an initial angle of 15.0 degrees.
After 1,000 seconds, its amplitude is reduced to friction by 5.50 degrees. What is the value of b/2m?

2. Relevant equations

In simple harmonic motion, a simple pendulum ---> 2pi times the square root of length over g constant.

3. The attempt at a solution
If it is released from an initial angle of 15 degrees, I believe I must do 1sin or cos15 degrees. If friction is involved, I guess I must use the sum of all forces which is tension and friction opposing one another? And what does "b" stand for?

2. Jan 25, 2010

### dacruick

b is a damping coefficient.

3. Jan 25, 2010

### MorganJ

A coefficient of what?

4. Jan 25, 2010

### dacruick

damping. Basically it represents how quickly friction damps the amplitude. It is usually if not always on the numerator with mass on the denominator. That is because the heavier something is, the harder it is to stop.

5. Jan 26, 2010

### MorganJ

Okay so 1 meter is my amplitude. I use 15 degrees for initial and afterwards 5.50 degrees. How do I go about this?

6. Jan 26, 2010

### dacruick

isn't one meter the length of the pendulum?

7. Jan 26, 2010

### MorganJ

Yes it is. Is this the equation: x=Ae exp -b/2m*t(cos(wt + phi))?