Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 ms-1 before the collision during which they stick together. What will be the velocity of the combined objects after collision?
Given,
Mass of first object, m1 = 1.5 kg
Velocity of first object, v1 = 2.5 m/s
Momentum of first object = m1 × v1
= 1.5 × 2.5
= 3.75 kg m/s
Mass of second object, m2 = 1.5 kg
Velocity of first object, v2 = - 2.5 m/s
So, Momentum of second object, m2 × v2
= 1.5 × (-2.5)
= - 3.75 kg m/s
So, Total momentum = 3.75 + (-3.75)
= 0 kg m/s (i)
Combined mass = m1 + m2
= 1.5 + 1.5
= 3.0 kg
Let, the velocity of the combined objects after collision will be v m/s.
Total momentum = (m1 + m2) × v
= 3.0 × v (ii)
We know that,
According to the principle of conservation of momentum:
Total momentum before collision = Total momentum after collision
0 = 3.0 × v
v = 
= 0 m/s
Therefore, the velocity of the combined objects after the collision will be 0 m/s.