Use the kinematic equation (v = u + at)
Rearrange for initial velocity: (u = v – at)
If displacement is known, use (s = ut + tfrac{1}{2}at^2)
Rearrange for initial velocity: (u = dfrac{s – tfrac{1}{2}at^2}{t})
If final velocity and displacement are known, use (v^2 = u^2 + 2as)
Rearrange for initial velocity: (u = pmsqrt{v^2 – 2as})
If momentum and mass are known, use (p = mv)
Rearrange for initial velocity: (u = dfrac{p}{m}) when the initial momentum is given
If using graphs, take the velocity at (t = 0) as the initial velocity
Use consistent units before substituting values
Choose the correct sign based on the direction of motion