SI units

The seven base units are the metre, kilogram, second, ampere, kelvin, mole and candela. Everything else in AP Physics is derived from them: $1\ \text{N} = 1\ \text{kg}\cdot\text{m/s}^2$, $1\ \text{J} = 1\ \text{N}\cdot\text{m}$, $1\ \text{W} = 1\ \text{J/s}$, $1\ \text{Pa} = 1\ \text{N/m}^2$.

Each AP table of information carries a short list of unit symbols. The AP Physics 1 list is hertz, joule, kilogram, meter, newton, pascal, second and watt. AP Physics 2 adds ampere, coulomb, degree Celsius, electron volt, farad, kelvin, mole, ohm, tesla and volt.

Why it costs marks: the sheet equations assume SI throughout, so a mass in grams, a length in centimetres or a volume in litres has to be converted first. Substituting $500\ \text{g}$ into $K = \tfrac{1}{2}mv^2$ gives an answer a thousand times too large, and it is not obviously wrong on the page.

The CED defines the free-response task verb Calculate as performing mathematical steps to arrive at a final answer, "including algebraic expressions, properly substituted numbers, and correct labeling of units and significant figures". Units are part of the answer, not decoration.

Degrees are the exception to watch: AP trigonometry is in degrees, while the kelvin, not the degree Celsius, is the base temperature unit.