Inelastic collision between two footballs players on ice

[irishbob]

Homework Statement

An American football game has been canceled because of bad weather in Cleveland, and two retired players are sliding like children on a frictionless ice-covered parking lot. William 'Refrigerator' Perry, mass 162 kg, is gliding to the right at 7.41 m/s, and Doug Flutie, mass 81.0 kg, is gliding to the left at 11.0 m/s along the same line. When they meet, they grab each other and hang on.
(a) What is their velocity immediately thereafter?
1.273 m/s

(b) What fraction of their original kinetic energy is still mechanical energy after their collision?

Homework Equations

KE_i=KE_f*c? This is kind of my issue.
KE_i is initial kinetic energy, KE_f is final kinetic energy, and c is a constant.

The Attempt at a Solution

Well I'm trying for the fraction of the energy:
Sum(KE_i)=0.5*162kg(7.41m/s)^2 + 0.5(81kg)(-11m/s)^2
=9348.0561=.5(162+81)kg(1.273m/s)^2c=KE_f*c
So I solved for c and got 6.890. Problem is, I have no idea what to do with it. Am I approaching this the right way?

 

[PhanthomJay]

You are getting the wrong answer due to your math and partly due to your approach. How did you get c=6.89? Anyway, what is the final mechanical energy (without any constant)? What is the initial kinetic energy? The final mechanical energy is a small percentage of the initial kinetic energy.

 

[irishbob]

Got the correct answer. Thanks! I don't know why I was doing it that way.

 

[PhanthomJay]

OK, and welcome to Physics Forums!

 

[irishbob]

Thanks!
I'm a long time lurker, first time poster.