Question

A body of mass 300g kept at a rest breaks into two parts due to internal forces. One part of mass 200g is found to move at a speed of 12m/s towards the east. What will be the velocity of the other part.

Answer 1

m1v1+m2v2=MV
m1v1=m2v2=mv
200*12+100v=0
-200*12/100=v
v=-24m/s

so th other part will move in west direction with 24m/s

Answer 2

Initial Momentum = 0
and Final will also be zero
mass of other part= 100g and let its velocity be x
100x + 200*12 = 0
x = -24
That means with a speed of 24m/s in opposite direction ...