Kinetic Energy = 1/2 m v²

m = mass (kg)

v = speed (m/sec)

example: The KE of a bullet of mass 50 grams moving at 400 m/sec

KE = 1/2 x (50x10^-3 kg) x (400 m/sec)² = 4000 joules

Q: Which is greater, the kinetic energy of a 100 gram tennis ball moving at 2 x 10⁸ cm/sec (about 10% of the speed of light) or a 5 x 10⁶ gram truck moving at 20 cm/sec?