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?
Let the two object be A and B.
Mass of object A, m1 = 1.5 kg
Mass of object B, m2 = 1.5 kg
Velocity of object A before collision,
u1 = -2.5 ms-1
Velocity of object B before collision,
u2 = -2.5 ms-1
∴ Total momentum of object A and B before collision = m1u1 + m2u2
= 1.5 x 2.5 - 1.5 x 2.5 = 0
Mass of combined object after collision
= (m1 + m2) = 3.0 kg
Let velocity of combined object after collision = V ms-1
∴ Total momentum of combined object after collision = (m1 + m2)V = (3V)kg ms-1
According to the law of conservation of momentum,
Momentum after collision = Momentum before collision
i.e., 3V = 0 or V = 0