Kinetic Energy Calculator
Find the kinetic energy of a moving object, or the speed or mass behind a given energy, with KE = ½mv² in any units.
KE = ½ m v²
Solve for
KE
Kinetic energy
J
1 sig figs: 100000
≡
Same value in
0.1447 MJ · 34,580 cal · 34.58 kcal
- Rearrange: KE = ½ m v²
- Substitute: m = 1500 kg, v = 50 km/h (converted to SI units first).
- Result: KE = 144,676 J, rounded to 1 significant figures because the least precise input has 1.
Speed is squared: see what that means
Going 1× as fast carries 1× the kinetic energy.
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0/1500
Where kinetic energy goes
Energy is conserved. A falling object turns potential energy into kinetic energy (mgh = ½mv², so v = √(2gh)). Brakes turn kinetic energy into heat. The work–energy theorem says the net work done on an object equals its change in kinetic energy.
Frequently asked questions
What is the kinetic energy formula?
KE = ½mv², with m in kg and v in m/s giving joules. A 1500 kg car at 50 km/h (13.9 m/s) has ½ × 1500 × 13.9² = 145 kJ.
Why does doubling speed quadruple kinetic energy?
Because v is squared: (2v)² = 4v². That is why a car at 100 km/h needs roughly four times the braking distance of the same car at 50 km/h: the brakes must remove four times the energy.
How do I find speed from kinetic energy?
Rearrange: v = √(2KE ÷ m). Choose “Speed” under “Solve for” above.
Can kinetic energy be negative?
No. Mass is positive and v² is never negative, so KE ≥ 0. Direction does not matter for kinetic energy.