Does Kinetic Energy Loss Equation Hold When Both Objects Are Moving?

[MotoPayton]

http://hyperphysics.phy-astr.gsu.edu/hbase/inecol.html

When a block in motion(M1) collides with a a stationary object (M2) in a perfectly inelastic collision, the fraction of KE final/KE initial can be modeled as M2/M1+M2.

My question is if M2 has to be stationary for this equation to work.

If both objects are moving before the collide in a perfectly inelastic collision does the ratio of lost kinetic energy still hold?

 

[Doc Al]

My question is if M2 has to be stationary for this equation to work.

Yes.

If both objects are moving before the collide in a perfectly inelastic collision does the ratio of lost kinetic energy still hold?

It's a bit more complicated when both blocks are initially moving. But it's easy enough to work it out.

 

[MotoPayton]

I ran the math and it makes sense now.

The only reason we use the M1/M1+M2 is because it is the only ratio of energies that has a simple mathematical form.

 

[Doc Al]

The only reason we use the M1/M1+M2 is because it is the only ratio of energies that has a simple mathematical form.

Yes. It's a special case that is particularly easy to deal with.