Question

Which will have more inpact on kinetic energy by doubling mass or by doubling velocity and why ?

Answer 1

doubling velocity as k.E. depends on square of velocity

Answer 2

According to
$ke = \frac{1}{2} \times mv {}^{2}$
the formuale If you double the velocity it will have more impact on kinetic energy as KE is proportional to square of velocity