Kinetic Energy Calculator

How do I solve for mass or speed instead of energy?

Enter the two values you know and put 0 in the one you want. Mass 10 and energy 125 gives a speed of 5.0000 m/s, and speed 5 with energy 125 gives a mass of 10.0000 kg. Leaving all three non-zero is treated as a request for energy: the energy you typed is ignored and recomputed from mass and speed.

Why does it say "Enter at least two values"?

Because zero is the "solve for this" marker, a genuinely zero quantity cannot be used. A body with mass 10 kg at 0 m/s and 0 J of energy triggers the message instead of a result of 0 J. Kinetic energy at rest is simply 0 without needing a tool.

What units does it use?

Kilograms, metres per second and joules. The output also repeats energy in kilojoules, shows speed in km/h (multiplied by 3.6) and gives momentum in kg·m/s. If your speed is in km/h, divide by 3.6 first: 100 km/h is 27.78 m/s.

Can speed be negative?

Yes, as a direction. Mass 10 kg at -5 m/s still gives 125 J, because the speed is squared, but the momentum shows -50 kg·m/s. Mass and kinetic energy must be positive when entered as inputs; negative mass is rejected, as is negative energy when solving for speed or mass.

How does doubling speed change stopping distance?

With a constant braking force, the work needed to stop equals the kinetic energy, so stopping distance grows with the square of speed. A 1500 kg car at 100 km/h carries 578796.3 J in the tool, four times the 144699.075 J at 50 km/h, and so needs four times the braking distance.

Is kinetic energy the same as momentum?

No. Momentum p = mv scales linearly with speed, energy ½mv² with its square. They are related by KE = p² ÷ 2m. A 0.145 kg ball at 40 m/s has 116 J of energy and 5.8 kg·m/s of momentum.

Does it include rotation or relativity?

No. It treats the body as a point mass moving in a straight line at everyday speeds. A rolling wheel also stores rotational energy, and near the speed of light the ½mv² formula no longer applies.