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?