# Freefall angular momentum

1. Oct 9, 2009

### briteliner

1. The problem statement, all variables and given/known data
a mass drops from rest without air resistance, starting from coordinates x=xo, y=yo, z=0. compute its angular momentum about origin at time=t. compare it to the torque on the mass. repeat this, but pick your origin for the angular momentum and torque about the point (x,y,z)=(2xo, 0,0).

2. Relevant equations
F=dp/dt

3. The attempt at a solution
gravity is the only force so mg=dp/dt. separating and integrating, mgt=p. this is way too simple, how should i attack this problem? i feel that i am not given enough information

2. Oct 9, 2009

### RoyalCat

$$\vec L= \vec R\times \vec P$$

$$\frac{d\vec L}{dt}=\Sigma \vec \tau$$

These should straighten things out for you. You found the linear momentum of the object, now find the angular momentum.

Last edited: Oct 9, 2009
3. Oct 10, 2009

### briteliner

but how? what is r and what is p with the info i am given?

4. Oct 10, 2009

### RoyalCat

$$\vec R$$ is the distance between the object and the point about which you're measuring the angular momentum and torques.

$$\vec P$$ is the linear momentum of the mass.

$$\Sigma \vec \tau$$ is the net torque on the mass.

What I posted was the definition of angular momentum, I am surprised you aren't familiar with it.

The second formula relates torque with angular momentum.