Question

How fast would the car need to go to double its kinetic energy? 12 m/s?

Answer 1

The car is traveling at v=12m/s. Kinetic energy is given by this formula:
$E_k=\frac{mv^2}{2}$
We can see that if the kinetic energy depends on the speed quadratically.  This means that if you want to increase the kinetic energy x times you would have to increase speed $\sqrt{x}$ times. We conclude from this that car would have to go:
$v'=\sqrt2v=\sqrt2\cdot 12=16.97\frac{m}{s}$