Kinetic energy calculator

The energy of a moving object, or the mass or speed that gives a certain energy.

Formula Science & engineering

Kinetic energy

Rounded for display

In kilojoules: ≈ 144.6759 kJ
Momentum: ≈ 20,833.3333 kg·m/s

How it works

Kinetic energy is half the mass times the speed squared. Because speed is squared, doubling the speed quadruples the energy, which is why braking distances grow so quickly.

The calculator converts the speed to metres per second first, so the energy comes out in joules. Rearranging gives m = 2E ÷ v² and v = √(2E ÷ m). This is the classical formula, accurate well below the speed of light.

Formula

KE = ½ × m × v²
m = 2 × KE ÷ v²
v = √(2 × KE ÷ m)
p = m × v

Worked example

A 1500 kg car at 50 km/h (13.89 m/s) has KE = ½ × 1500 × 13.89² ≈ 144,676 J, about 144.7 kJ. At 100 km/h it has four times as much.

Questions people ask

Why does doubling speed quadruple the energy?

Energy depends on the square of the speed: (2v)² = 4v².

What is a joule?

The SI unit of energy: the work done by a force of 1 newton over 1 metre. 1 kWh is 3.6 million joules.

Can kinetic energy be negative?

No. Mass is positive and speed is squared, so kinetic energy is always zero or more.