A particle at rest suddenly disintegrates into two particles of equal masses which start moving. The two fragments will:

As Fext = 0, hence P1→ + P2→ = constantBecause the system was at rest initially, henceP1→ + P2→ = 0 or P2→ = -P1→ or m2v2→ = -m1v1→Because m1 = m2 hence v2 →= -v1→