How can I calculate kinetic energy from mass and speed?

Use the introductory formula for translational kinetic energy:

KE = ½mv²

Here, m is mass and v is speed. The important detail is that the speed is squared: calculate v × v before multiplying by the mass and taking half. This is the classical, nonrelativistic model for an idealized object moving from place to place; it is not the relativistic formula. [S1]

For the units to come out directly in joules, put mass in kilograms and speed in metres per second. In those units, the calculation gives kg·m²/s², which is equivalent to a joule. [S1]

Sure. Keep the speed in parentheses so it is clear that the whole value is squared:

1. Write the values: m = 2 kg, v = 3 m/s.
2. Substitute: KE = ½ × 2 × (3)².
3. Square the speed: 3² = 9.
4. Calculate: ½ × 2 × 9 = 9.
5. State the result with units: KE = 9 J.

The joule check works because kg·m²/s² is equivalent to J. This matches the worked example in the cited physics summary. [S1] If you instead calculate ½ × 2 × 3, you have missed the square and will get the wrong result.

Not if you want the answer directly in joules. Convert the measurements first: change the mass to kilograms and the speed to metres per second, then use the converted values in KE = ½mv². With those units, the result is expressed in joules. [S1] For instance, write your conversion results as m = [mass in kg] and v = [speed in m/s]; then calculate ½ × [mass in kg] × ([speed in m/s])².

This helps avoid mixing units inside one calculation. Keep the speed in parentheses when squaring it, and label the final energy in joules. If you are unsure about a conversion, check it separately before substituting; the formula alone does not confirm that an input measurement or conversion is correct.

The formula here is explicitly the nonrelativistic translational model, not a relativistic calculation. [S1] The cited material establishes that distinction but does not provide the relativistic formula or a speed threshold for choosing between models, so do not use this guide to decide a high-speed case. For a rough speed estimate, you can still show the calculation as an estimate, but the result depends on the value you enter; it does not make an uncertain measurement exact.

Reusable setup:

m = [mass in kg] v = [speed in m/s] KE = ½ × [m] × ([v])² KE = [calculated value] J

Before reporting it, verify the units, square the entire speed value, and include the assumptions that the object is treated with this introductory model and that your inputs are estimates if applicable.