Find the components along the x, y, z axes of the angular momentum l of a particle, whose position vector is r with components x, y, z and momentum is p with components `p_(x), p_(y) and p_(z)`. Show that if the particle moves only in the x-y plane the angular momentum has only a z-component.

Explanation

`l_(z)=xp_(y)-yp_(x),l_(x)=yp_(z)-zp_(y),l_(y)=zp_(x)-xp_(z)`