Quick answer
This kinetic energy calculator uses KE = ½mv² to find the energy of a moving object. It can also work backwards to find the mass or the speed. Results are in joules, with the formula and substitution shown.
Kinetic energy (KE = ½mv²) calculator
How to Use the Kinetic Energy Calculator
- Choose kinetic energy, mass or velocity.
- Enter the other two values: mass in kg, speed in m/s, energy in J.
- Press Calculate.
Kinetic Energy Formula
KE = ½mv²
KE is kinetic energy in joules (J), m is mass in kg and v is speed in m/s. Because v is squared, doubling the speed makes the kinetic energy four times bigger.
Rearranged: m = 2KE ÷ v² and v = √(2KE ÷ m). Our kinetic energy guide shows where the formula comes from and how it links to work done.
Worked Example
Worked example: a cyclist
Question: A cyclist and bike have a combined mass of 80 kg and travel at 8 m/s. What is their kinetic energy?
- Choose “Kinetic energy (KE)”.
- KE = ½ × 80 × 8².
- KE = ½ × 80 × 64 = 2,560 J.
Answer: The kinetic energy is 2,560 J, or 2.56 kJ.
Why Speed Matters So Much
A car at 60 km/h has four times the kinetic energy of the same car at 30 km/h. The brakes must remove all of that energy to stop the car, so stopping distances grow much faster than speed. This is one of the main reasons speed limits near schools are low.
Practise: try these kinetic energy MCQs with answers and step-by-step explanations.
Frequently Asked Questions
What is the formula for kinetic energy?
Kinetic energy equals half the mass times the speed squared: KE = ½mv².
What unit is kinetic energy measured in?
Kinetic energy is measured in joules (J). 1 J = 1 kg·m²/s².
Can kinetic energy be negative?
No. Mass is positive and speed squared is never negative, so kinetic energy is always zero or positive.