1. The problem statement, all variables and given/known data A car starts from rest and accelerates uniformly at 3.0 m/s2. A second car starts from rest 6.0 s later at the same point and accelerates uniformly at 5.0 m/s2. How long does it take the second car to overtake the first car? 2. Relevant equations 3. The attempt at a solution So let [itex]t[/itex] represent the time since the FIRST car, Car A has taken off. Let [itex]T[/itex] represent the time since the SECOND car, Car B has taken off. Note that [itex]T = t - 6[/itex]. [itex]x_A(t) = (3/2)t^2 [/itex] [itex]x_B(t) = (5/2)(t-6)^2[/itex] Let x_A(t) = x_B(t) you find, t = 26.618, So I say that 26.618 seconds after the first car starts, the second car overtakes it. The correct answer is 21 seconds. 26.618 - 6 = 20.618 =~ 21. My point is, they dont explain from which "frame of reference" you should point out your time, then why isnt t = 26.618 correct?