⚡ Kinetic Energy Calculator

KE = ½mv² — Solve for kinetic energy, mass, or velocity.

Solve for

Mass (kg)

Velocity (m/s)

Kinetic Energy (J)

—J

How to Use This Calculator

Select what to solve for (kinetic energy, mass, or velocity), enter the two known values, and the calculator returns the result instantly. Mass goes in kilograms and velocity in m/s. Common conversions: 60 km/h = 16.67 m/s, 100 km/h = 27.78 m/s.

Pick the variable to solve for from the dropdown: Kinetic Energy (J), Mass (kg), or Velocity (m/s).

Enter mass in kilograms. A person weighing 70 kg, a car at 1200 kg, a tennis ball at 0.058 kg.

Enter velocity in m/s. Divide km/h by 3.6 to convert. A car at 90 km/h is 25 m/s.

Read the kinetic energy in joules. Large values are also shown in kilojoules for convenience.

Kinetic Energy Formula

KE = ½ × m × v² m = 2 × KE / v² v = √(2 × KE / m) KE in joules (J), m in kg, v in m/s

Velocity is squared in the formula, which makes it the dominant factor. Doubling mass doubles KE. Doubling velocity quadruples KE. This is the reason why road accident severity increases so sharply with speed, and why speed limits matter more than car weight for crash energy.

Worked Examples

Person 70 kg jogging at 3 m/sKE = ½ × 70 × 9 = 315 J

Car 1200 kg at 60 km/h (16.67 m/s)KE = ½ × 1200 × 278 = 166,800 J = 166.8 kJ

Same car at 120 km/h (double speed)KE = 667,200 J = 667.2 kJ (4× more)

Cricket ball 0.156 kg at 40 m/s (144 km/h)KE = ½ × 0.156 × 1600 = 124.8 J

Where This Comes Up in Real Life

Crumple zones in modern cars are designed to absorb kinetic energy during a crash. At 60 km/h, a 1500 kg car has KE = ½ × 1500 × 16.67² = 208,375 J. The crumple zone must absorb all of this energy over a distance of about 0.5 m, requiring an average force of 208,375 / 0.5 = 416,750 N. Engineers tune the crumple geometry to keep deceleration forces below the human injury threshold.

Kinetic energy also matters in ballistics and sports equipment design. A golf driver transfers kinetic energy from the clubhead to the ball during a collision that lasts less than half a millisecond. The clubhead mass is about 0.2 kg traveling at 45 m/s, giving KE = ½ × 0.2 × 2025 = 202.5 J. The efficiency of energy transfer during impact determines how far the ball travels, which is why manufacturers obsess over coefficient of restitution values in their club designs.

Frequently Asked Questions

What is kinetic energy?

Kinetic energy is the energy of motion. KE = ½mv², where m is mass (kg) and v is velocity (m/s). Unit: Joule (J).

How does doubling speed affect KE?

KE is proportional to v². Doubling speed quadruples kinetic energy.

What is the unit of kinetic energy?

The SI unit is the Joule (J = kg·m²/s²).

How is KE related to work?

Work-energy theorem: net work done on an object equals its change in kinetic energy. W = ΔKE.

Example: 2000 kg car at 30 m/s?

KE = ½×2000×30² = ½×2000×900 = 900,000 J = 900 kJ.