A ball of mass 0.6 kg moves at 12 m/s. Find its kinetic energy.

Kinetic energy $KE = \tfrac{1}{2}mv^2$: twice the speed gives four times the energy. The work done on an object equals the change in its kinetic energy; a brake force $F$ stops it in $d$ when $F \times d = \tfrac{1}{2}mv^2$.