How to get power of collision?

Example what i want:

sqrdestructPower = 5;

if(collisionAnotherObject && sqrdestructPower > relativevelocity.sqrmagnitude )

destroy object.

The closest thing I can think of that matches that is kinetic energy (KE), which can be calculated with:

KE = 0.5*mass*velocty^2

But why not just do it just like that example? The power is just a variable with a value of 5, which you then compare with the velocity^2, or just like your other topic.

The only new thing would be the relative velocity I guess, but that's just a simple vector subtraction of one velocity from another.