# What role does the center of mass play in this situation? (electric potential)

Four masses $10\ \mathrm{g}$ each are tied together by $10\ \mathrm{cm}$ strings to make a square as shown. Two of the masses carry a charge of $2\ \mathrm{\mu C}$. The string between the two charged masses is cut and the system begins to move. What is the maximum speed of the masses in $\mathrm{m/s}$? Do not consider gravity or friction. You can imagine the masses to be on a horizontal frictionless table.

The answer key says that the two charges repel and they go on an infinite loop of oscillation. And it also points out that the center of mass does not move. What does the center of mass have anything to do with this problem?

• Hi and welcome to the Physics SE! Please note that this is not a homework help site. Please see this Meta post on asking homework questions and this Meta post for "check my work" problems. Apr 14 '16 at 14:23
• I'm self-studying physics and I'm not asking you guys to do my homework problem. This is a problem from an online course on EDX and the answer key is also available on the website. Sorry if I violated any rules of the forum. Apr 14 '16 at 14:29
• Comments are not for extended discussion; this conversation has been moved to chat. Apr 15 '16 at 7:15