# Homework Help: Rocket Pendulum Problem

1. Apr 6, 2008

### iwonde

1. The problem statement, all variables and given/known data
A rocket is accelerating upward at 4.00 m/s^2 from the launchpad on the earth. Inside a small 1.50-kg ball hangs from the ceiling by a light 1.10-m wire. If the ball is displaced 8.50 degrees from the vertical and released, find the amplitude and period of the resulting swings of the pendulum.

2. Relevant equations
T = 2pi \sqrt{L/g}
\omega = /sqrt{g/L}
x = Acos(\omegat + \phi)

3. The attempt at a solution
I think this is a simple pendulum problem.

T = 2pi /sqrt{1.1/4} = 3.29 s, I relplaced g with the upward acceleration of the rocket.

I'm trying to solve for A from the equation that I have for x, but I don't have t.

2. Apr 6, 2008

### DavidWhitbeck

You identified the wrong acceleration. The pendulum would fall at a rate of g if the rocket was unaccelerated, right? Your procedure would indicate otherwise. You would formally argue this from Newton's 2nd Law, but I'll just tell you that you should replace g with a + g. That way (a) if a = 0 you get back what you usually have, and (b) if a = -g the rocket is in freefall, the pendulum does not work and you get an infinite period.