Calculator
Kinetic energy125 J
Method, variables and units
Kinetic Energy Calculator
Formula: E_k = 1/2 m v^2
Assumption: The calculation uses classical mechanics.
Worked example
Kinetic Energy Calculator
A 10 kg object moving at 5 m/s has 125 J of kinetic energy.
Kinetic energy of everyday objects
| Object | Mass (kg) | Speed (m/s) | Kinetic energy |
|---|---|---|---|
| Tennis ball serve | 0.058 | 50 | 73 J |
| Sprinter (80 kg) | 80 | 10 | 4,000 J |
| Cyclist with bike (90 kg) | 90 | 8 | 2,880 J |
| Car (1,500 kg) at 50 km/h | 1,500 | 13.9 | 144,676 J |
| Car (1,500 kg) at 100 km/h | 1,500 | 27.8 | 578,704 J |
Because speed is squared, doubling speed multiplies kinetic energy by four. The same car carries about 579 kJ at 100 km/h but only 145 kJ at 50 km/h. That energy has to be removed by the brakes as heat, which is why stopping distance grows much faster than speed. For comparison, 1 kWh is 3.6 million joules.
Common mistakes
- Entering speed in km/h: convert to m/s first by dividing by 3.6, otherwise the answer is 12.96 times too large.
- Forgetting the ½: E = m × v² is twice the kinetic energy.
- Adding energies of objects moving in different directions as vectors: energy is a scalar and simply adds.