Free · Mechanics and material properties

Classical Kinetic Energy from Mass & Speed

Calculate translational kinetic energy, mass or the nonnegative speed corresponding to an entered energy.

Formula & worked example
Private in your browser
No signup

Go to tool

Calculator inputs

Loading calculator…

How to use this calculator

Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 2 kg object moving at 3 m/s has kinetic energy 9 J. Reversing its direction leaves that energy unchanged.

Kinetic energy = mass × velocity² ÷ 2

Worked example

Enter these known values and leave the other values blank.

Mass: 2 kg
Velocity / nonnegative inferred speed: 3 m/s

Classical translational kinetic energy: 9 J

Assumptions and limitations

Mass and energy are nonnegative. A supplied signed velocity is squared, so reversing direction preserves energy.
When energy and positive mass determine velocity, the displayed inverse is the nonnegative speed; direction is not inferred.
The classical approximation is intended for speeds small compared with light speed. It excludes rotational energy and relativistic effects.
Zero mass and zero energy do not uniquely determine speed.

Common questions

Why does negative velocity give positive energy?

Velocity is squared in the energy expression, so its direction does not change the energy.

Which direction does the inverse result describe?

None. The inverse result is a nonnegative speed magnitude.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

Explore mechanics and material properties or browse all physics calculators.