Thanks for the comment, Alejandro! I stopped thinking in terms of energy, and was able to solve this problem fairly easily.
(The terms in bold are vectors)
I) After the instantaneous impulse, there will be no net external force acting on the system. Thus, the linear momentum must be conserved...
Homework Statement
Four equal discs of mass ocuppy the vertices of a square frame made by four rigid bars of length and negligible mass. The frame is at rest on a horizontal table, and it can move with negligible friction. An instantaneous impulse is transmitted to one of the masses, in the...