Calculating Kinetic Energy in Elastic Collisions: Hammer and Nail Problem

[Cassie]

The collision between a hammer and a nail can be considered to be approximately elastic. Estimate the kinetic energy acquired by a 12 g nail when it is struck by a 550 g hammer moving with an initial speed of 5.0 m/s.

I thought I tried every combination of (1/2)(m+M)V^2 ... apparently except for the one I need. Any help on a step I am missing?

 

[learningphysics]

use conservation of momentum, as well as conservation of kinetic energy.

show your steps.