why are the units of acceleration m/s2
Metre per second squared As acceleration, the unit is interpreted physically as change in velocity or speed per time interval, i.e. metre per second per second and is treated as a vector quantity.
Equations for a falling body Near the surface of the Earth, the acceleration due to gravity g = 9.81 m/s2 (meters per second squared; which might be thought of as "meters per second, per second", or 32.2 ft/s2 as "feet per second per second") approximately. For other planets, multiply g by the appropriate scaling factor. A coherent set of units for g, d, t and v is essential. Assuming SI units, g is measured in meters per second squared, so d must be measured in meters, t in seconds and v in meters per second.