KE = 0·5 x 500 x 122 = 36,000J. (See also the KE of a Car). The kinetic energy of an object is directly proportional to its mass. This means that if you double the mass you also double the kinetic energy (for the same velocity). The kinetic energy of an object is proportional to its velocity squared. This means that if you double the velocity, you multiply the kinetic energy by 22 = 4 (for the same mass). This has implications for the braking distance of a car.