# Calculate angular momentum? I almost got the right answer but it's wrong Help!

1. Nov 19, 2012

### riseofphoenix

Calculate angular momentum? I almost got the right answer but it's wrong!! Help!

This is what I did for part a...

1. What is given

Particle
mp = 0.450 kg
r = 1 m

Stick
ms = 0.125 kg
r = 0.5 m

2. Angular momentum is conserved (Linitial = Lfinal) due to a lack of friction

0 = Lfinal

L = Iω
L = (mr2
L = (0.450 + 0.125)(0.52)(2)
L = (0.575)(0.25)(2)
L = 0.2875

Help!!!!

2. Nov 19, 2012

### Spinnor

Re: Calculate angular momentum? I almost got the right answer but it's wrong!! Help!

The formula you use for I is only good for a point mass. For a distributed mass (the meter stick) you must use a different formula, see,

http://www.physics.uoguelph.ca/tutorials/torque/Q.torque.inertia.html

and use the appropriate formulas for the slender rod.

So I_total = I_meter stick + I_mass

3. Nov 19, 2012

### TSny

Re: Calculate angular momentum? I almost got the right answer but it's wrong!! Help!

?? This problem does not involve conservation of angular momentum.

You need to find the moment of inertia of the stick either by calculation using calculus or by consulting a table.