A comet has broken into three pieces of masses m1, m2, m3 with velocities
v1, v2 and v3 respectively. Find the velocity v0 of the comet before it has
broken.
Yes, but remember that this is a vector equation, so the momenta add vectorally. (ie. if this is a problem in 2D then you actually have two equations:
$\displaystyle M*v_{0x} = m_1*v_{1x} + m_2*v_{2x} + m_3*v_{3x}$
and
$\displaystyle M*v_{0y} = m_1*v_{1y} + m_2*v_{2y} + m_3*v_{3y}$)
-Dan