Question

unit of time occurs twice in unit of acceleration why

Answer 1

Calculating acceleration involves dividing velocity by time — or in terms of units, dividing meters per second [m/s] by second [s]. Dividing distance by time twice is the same as dividing distance by the square of time. Thus the SI unit of acceleration is the meter per second squared.

Answer 2

velocity is distance / time and acceleration is increase of velocity with time.

Unit of displacement is unit of length, i.e. m.
Unit of velocity is unit of (length/time), i.e. m/s
Unit of acceleration is unit of (velocity/time), i.e. (m/s)/s = m/s2.
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