## College Physics (7th Edition)

Since, Kinetic energy =$\frac{1}{2}mv^{2}$ If we reduce mass by half, the Kinetic energy will be $\frac{1}{2}$ of initial Kinetic energy. If we reduce speed by half, the Kinetic energy will be $\frac{1}{4}$ of initial Kinetic energy. So, to decrease the Kinetic energy as much as we can, we should reduce the speed to half.