How to Calculate Kinetic Energy Percentage in Non-Elastic Collision?

[kbeyer]

Problem: A projectile (mass = 0.20 kg) is fired at and embeds itself in a target (mass = 2.50 kg). The target (with the projectile in it) flies off after being struck. What percentage of the projectiles' incident kinetic energy does the target (with the projectile in it) carry off after being struck?

 

[Clairefucious]

Energy is conserved. Kinetic energy in an elastic collision (where there is no conversion to any other sort of energy) remains the same.

 

[Redbelly98]

Welcome to PF, kbeyer.

This is not an elastic collision, so kinetic energy is not conserved.

So, what equation or equations do you know that deal with collisions?

edit added:
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