John Denker and Brian Whatcott have already adequately responded to
the questions asked about energy of/inside the system of rock and
moon.
As an addendum, consider computing the resulting speed of the rock
relative to the moon in the general case where the rock can have any
mass (not necessarily small compared to that of the moon) and may
initially be traveling with nonzero speed in an arbitrary direction
(ie. arbitrary initial velocity relative to the moon). Interestingly
enough, it turns out one can write a simple equation for the
resulting relative speed, Eq. (3) in the following:
which has some nice applications. If you would like some fun, try
deriving the formula for the relative speed before you look at that
reference for the answer. -Carl
(No novelty claimed in this reference of mine, but I think it's neat
and I hope I've summarized things more clearly than I've seen in some
other references.)
--
Carl E Mungan, Assoc Prof of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-5002 mailto:mungan@usna.eduhttp://usna.edu/Users/physics/mungan/