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Kinetic Energy Calculator

Find the kinetic energy of a moving object.

How it is calculated

Kinetic energy is the energy an object has because it moves: E = ½ × m × v². m is mass in kilograms, v is speed in metres per second and the result is in joules (J). Because speed is squared, doubling the speed quadruples the energy, while doubling the mass only doubles it. A negative velocity gives the same result as a positive one (only the speed matters, not the direction), but a negative mass is rejected. The result is rounded to two decimals. Relativistic speeds close to that of light are outside the scope of this classical formula.

Worked example

A car of 1,200 kg moving at 25 m/s (90 km/h). Square the speed: 25² = 625. Multiply by mass: 1,200 × 625 = 750,000. Take half: 375,000.00 J, or 375 kJ. If the speed rose to 50 m/s (180 km/h), the energy would be four times bigger, 1,500,000 J, which is why braking distance grows so quickly with speed.

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Common mistakes

  • Entering speed in km/h. The formula needs m/s, so 90 km/h must be converted to 25 m/s first; otherwise the answer is about 13 times too large.
  • Forgetting that velocity is squared and expecting energy to double when speed doubles.
  • Entering mass in grams or tonnes instead of kilograms.
  • Forgetting the factor ½ and getting twice the correct energy.

About this calculator

This calculator applies the classical mechanics formula KE = ½mv², where energy grows with the square of velocity — doubling speed quadruples the kinetic energy, not just doubles it. It's the same relationship that makes high-speed collisions so much more destructive than low-speed ones.

It's used by physics students solving textbook problems, automotive engineers estimating crash-impact energy for safety testing, ballistics enthusiasts calculating projectile energy, and roller-coaster designers checking that cars carry enough energy through a loop.

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