Hello, considering a Planet 1 and a Planet 2, where 1 is extremly heavier than 2 and 2 is going in Planet 1's orbit. Two questions 1) howto get the expression v = - G m2 m1 / r 2) if we consider the energy < 0, we can get to an expression as v < sqrt (2GM2 / r) howto get Vx and Vy for that V ? (r is the radius.) Hints and other help are welcome. Thanks.