In classical mechanics, kinetic energy is defined as the 1/2 mass times the square of speed. Derive a unit for energy starting with SI base units. Using SI prefixes, suggest a convenient unit for the kinetic energy of a car weighing 2500 pounds moving at 45 mi per hour and the kinetic energy of an electron moving at 35% of the speed of light (mass electron = 9.11×10^–31 kg, speed of light = 3.00×10⁸ m/s).