1. The problem statement, all variables and given/known data So my textbook states that F = ma = m(d2r/dt2) can be integrated to give r = r0 + tv0 when F = 0. 2. Relevant equations 3. The attempt at a solution I've tried rewriting it as F = m(dv/dt) and integrating that to give Ft = mv + c but this is obviously not in the right form. I've also tried using F = dP/dt but that gives effectively the same answer as above. I have no idea how to get the solution given!