Mass of one of the object, m1=1.5 kg
Mass of the other object, m2 = 1.5 kg
Velocity of m1 before collision, u1 = 2.5 ms−1
Velocity of m2, moving in opposite direction before collision, u2 = -2.5 ms−1
Let v be the velocity of the combined object after 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 ms−1