Calculate kinetic energy using KE = ½mv². Solve for mass or velocity too. Covers classical mechanics, unit conversion, and real-world examples from cars to spacecraft.
Kinetic energy KE = ½mv², where m is mass in kilograms and v is velocity in metres per second. The result is in joules (J). Doubling speed quadruples kinetic energy because velocity is squared.
The SI unit is the joule (J). 1 J = 1 kg·m²/s². Larger amounts are expressed in kilojoules (kJ), megajoules (MJ), or kilowatt-hours (kWh, used for energy storage).
A 1,400 kg car at 100 km/h (27.78 m/s): KE = 0.5 × 1400 × 27.78² = approximately 540,000 J (540 kJ). This is the energy that must be dissipated when braking to a stop.
Braking distance is proportional to kinetic energy, which increases with the square of speed. At 100 km/h you have 4 times the kinetic energy of 50 km/h, so roughly 4 times the braking distance.
A typical 9mm bullet (7g, 370 m/s): KE = 0.5 × 0.007 × 370² = 479 J. A high-velocity rifle bullet can have 3,000-4,000 J. Kinetic energy determines the stopping power and penetration of projectiles.
Kinetic energy is the energy of motion (½mv²). Potential energy is stored energy due to position (mgh for gravitational). At the top of a roller coaster, energy is mostly potential. At the bottom, it is mostly kinetic.
No. Because KE = ½mv² and both mass and velocity squared are always non-negative, kinetic energy is always zero or positive. An object at rest has zero kinetic energy.