Two objects, each of mass 1.5kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5ms⁻¹ before the collision during which they stick together. What will be the velocity of the combined object after collision?

Given : m1=m2=1.5 kg
u1=2.5 ms⁻¹
u2=-2.5 ms⁻¹ (since the objects are moving in opposite directions)
Total mass of the combined system, M=m1+m2=2×1.5=3kg
Let the velocity of the combined system after the collision be v
Applying conservation of momentum before and after the collision :
m1u1 + m2u2 = Mv
1.5×2.5 + 1.5×(-2.5) = 3v
3.75 - 3.75 = 3v
0 = 3v
∴ v = 0