Question

A sphere of mass 5kg having a velocity 4m/s and another sphere of mass 4kg having a velocity of 2m/s in the opposite direction. After the collision they stick each other and move with common velocity, their total initial momentum of the system is

Answer 1

M1u1+M2u2

5×4+4×[-2]

12kgm/s

Answer 2

Here,

Initial momentum = m1*v1+m2*v2

=5*4-4*2

[(-ve) sign is due to opposite in direction]

=12kgm/s

After the collision,

Initial momentum = final momentum

m1*v1 - m2*v2 = (m1+m2) *v

5*4-4*2 = (5+4)*v

12 = 9*v

=> v = 1.33m/s

That's your solution hope this solution will help you to understand