I have made this point exactly. However, on a practical note, the 'force" of the hammer would be insuff to overcome the intertia of the earth, of bring it out of orbit. However, when they bring out that calculation to show that there forces exactly equal out, ask them this in the classic "twobody" problem, is the mass of the "other" object of no inport at all?
But is this not better for GQ?
