Is This a Case of Inelastic Collision?

[jemerlia]

Homework Statement

Two wooden blocks of mass 8 kg and 4 kg respectively approach
each other from opposite directions on a smooth level surface at a
relative speed of 16 m s^1 . After a head-on collision they separate
at a relative speed of 6 m s^1 . The initial velocity of the 8 kg block
was 7 m s -1 North. Find the velocity of
(a) the 4 kg block immediately before the impact;
(b) the 8 kg block immediately after the impact;
(c) the 4 kg block immediately after the impact.

Homework Equations

f=ma
F x delta T= delta P

For an elastic collision
va-vb = -(va'-vb')

The Attempt at a Solution

Part (a) is straightforward

Part (b) appears awkward because the collision seems inelastic because
the relative velocity after impact is different in magnitude to that before
impact and doesn't follow the relationship:
va-vb = -(va'-vb')

Am I correct in assuming the collision to be inelastic?
How does one approach a solution to problem (b)?

Help and guidance gratefully received.

 

[Doc Al]

Am I correct in assuming the collision to be inelastic?

Yes.

How does one approach a solution to problem (b)?

By making full use of the given information (the relative velocity after the collision) and applicable conservation laws (what's conserved?).