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 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?

Mass of one of the objects,m1 = 1.5 kg

Mass of the other object, m2 = 1.5 kg

Velocity of m1 before collision, u1 = 2.5 m/s

Velocity of m2, moving in opposite direction before collision, u2 = -2.5 m/s

The velocity of the combined object after collision

Let v be the velocity of the combined object after the collision. By the law of conservation of momentum,

Total momentum after collision = Total momentum before collision,

Or, (m1 + m2) v = m1u1 + m2u2

Or, (1.5 + 1.5) v = 1.5 (2.5) + 1.5  (-2.5) [negative sign as moving in opposite direction]

Or, v = 0

Thus, the velocity of the combined object after the collision is 0 m/s