Kinetic energy, KE, is modeled by the formula [tex]KE = \frac{1}{2}mv^2[/tex], where m is the mass in kg and v is the velocity in m/s.
In this scenario, mass and one-half are constant but the velocity changes.
You can see that by squaring twice the velocity, that is equal to four times the original KE. Therefore, the answer is 4k.