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## Homework Statement

A projectile of mass

*m*is launched with an initial velocity [PLAIN]https://www.webassign.net/images/boldv.gif[I]i[/I] [Broken] making an angle θ with the horizontal as shown below. The projectile moves in the gravitational field of the Earth. Find the angular momentum of the projectile about the origin when the particle is at the following locations. (Use the following as necessary:

*vi*, θ,

*m*, and

*g*for the acceleration due to gravity.)

(a) at the origin

(b) at the highest point of its trajectory

(c) just before it hits the ground

## Homework Equations

L=r x p

## The Attempt at a Solution

For (a) angular momentum is zero because there is no r.

I mean, the problem overall seems easy, but how on earth do I find r for the other two positions? The answer doesn't help with how this is found at all. Is there some sort of property or formula with symmetrical projectile motion?

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