1. The problem statement, all variables and given/known data Show that d=(9M/(4*pi*p))^1/3 is an approximation for the roche limit. Note that x/d <<1 with M = mass of the primary p = density of the secondary x= distance of a test particle from the center of the secondary (in part a) of the task one should give the motion equation for X. X is a particle that is situated at distance x from the center of the secondary (on a line that goes from the center of the secondary to the center of the primary) m = mass of the secondary 2. Relevant equations 3. The attempt at a solution In the critical point the tidal force excerted from the primary and the gravitational force that hold the secondary together are equal and therefore the secondary breaks. So I tried to put these forces equal and to solve the equation for d, but it did not work out.