# Rotation - Angular Momentum

## The Attempt at a Solution

I did it like this:

$$\vec{L}_{B \ wrt \ Ground} = \vec{L}_{B \ wrt \ A} + \vec{L}_{A \ wrt \ Ground}$$

$$\vec{L}_{B \ wrt \ A} = \vec{L}_{B \ wrt \ Ground} - \vec{L}_{A \ wrt \ Ground}$$

so

$$\vec{L}_{B \ wrt \ A} = mwd^2 \ - \ \frac{1}{4}mwd^2$$

$$\vec{L}_{B \ wrt \ A} = \frac{3}{4}mwd^2$$

why is my method wrong?

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tiny-tim
Homework Helper
hi cupid.callin!
$$\vec{L}_{B \ wrt \ A} = \vec{L}_{B \ wrt \ Ground} - \vec{L}_{A \ wrt \ Ground}$$
sorry, but this doesn't work at all

LA(B) = rAB x (vB - vA)

= (rOB - rOA) x ((vB - v0) - (vA - vA)) …

bits of that are the RHS of your equation, but that's all

Why is does not work,

Is it because the eqn i used relates velocity or acceleration of particle wrt to a non inertial particle or frame ???

tiny-tim