1D Elastic Collision?

Question

The particles in the figure below 
(m1 = 1.4 kg and m2 = 3.5 kg) 
undergo an elastic collision in one dimension. Their velocities before the collision are v1i = 12 m/s and v2i = −7.5 m/s. 
Find the velocities of the two particles after the collision. (Indicate the direction with the sign of your answer.) 
V1f ______ 
V2f ______ 

Answer 1

The mass of the particles are

m1 = 1.4 kg.

m2 = 3.5 kg.

The velocity of the m1 before collision is v1 = 12 m/sec

The velocity of the m2 before collision is v2 =  -7.5 m/sec

First the centre velocity is calculated

Therefore the velocities after collision are 

The velocity of the m1 after collision is .

The velocity of the m2 after collision is.

Therefore the velocities after collision are -15.8 m/sec and 3.644 m/sec.