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Kinetic Energy Calculator

Work out kinetic energy from mass and speed, or find the speed or mass from the energy, with momentum and the equivalent drop height.

Rules last checked 10 November 2026Every step shown

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kg

Kinetic energy

115.74 kJ

In joules
115,741 J
Momentum
16,666.7 kg·m/s
Same speed as falling from
9.84 m

1,200 kg moving at 50 km/h carries 115.741 kJ of kinetic energy, as much as it would gain falling 9.8 m.

How it's worked out

  1. Speed in m/s50 km/h × 0.2777813.889 m/s
  2. Kinetic energy½ × 1,200 kg × 13.889²115,741 J
  3. Drop height for the same speed13.889² ÷ (2 × 9.81)9.84 m
  • Energy grows with the square of speed: double the speed and the energy, and the distance needed to stop, go up four times.

How it is worked out

The speed is turned into metres per second first, then KE = ½mv². To find speed from energy, v = √(2 × KE ÷ m); to find mass, m = 2 × KE ÷ v². Momentum is mass × speed.

Questions people ask

How much kinetic energy does a car have at 50 km/h?

A 1,200 kg car at 50 km/h has about 115.7 kJ. At 100 km/h it has about 463 kJ, four times as much.

What is the kinetic energy formula?

KE = ½ × mass × speed², with mass in kilograms and speed in metres per second, giving joules.

Why does doubling speed quadruple the energy?

Because speed is squared. That is also why stopping distances grow so fast with speed: the brakes have four times as much energy to get rid of.

What does 'same speed as falling from' mean?

The height an object would have to fall, ignoring air resistance, to reach the same speed. 50 km/h is like falling about 9.8 m.

Formula and rules last checked 10 November 2026Written and tested by the CalculatorDex teamReport a problem