Hello all, I'm confused with the center of mass concept. Regard the following problem, we have a spring with negligible mass joined to two masses m1 and m2 (m1=m2) on a table without friction force. At t=0 a thrust Vo (initial velocity) is given to m2 with direction perpendicular to the spring direction (see figure adjoint). How are the velocities at t=0 seen from the center of mass? At t=0 the m1 velocity seen from the laboratory is zero but this particle isn't fixed on the table. Well, I guess that I should calculate the velocity of the center of mass as: Vcm = m1V1 + m2V2 / (m1 + m2) = m2V2 / (m1 +m2) = Vo / 2, since m1 and m2 are equals. So the initial situation is equivalent to give a thrust to the center of mass with velocity Vo/2, but how I know what are the velocities of m1 and m2 seen of the center of mass??? Can anyone help me? Thanks in advance.