Posted by Nathan on Tuesday, January 25, 2011 at 8:52pm.
Two cars adjacent to each other on a highway. The first car accelerates uniformly at 3m/s2 the moment the light turns green. The second car is moving at 18m/s and is beside the first car at the instant the light changes and continues driving with a constant velocity. When are the cars side by side again?

physics  drwls, Tuesday, January 25, 2011 at 8:59pm
Write equations for position from the light (X) vs time (t) and set them equal to each other.
Solve for t.
X1 = (a/2) t^2 = 1.5 t^2
X2 = 18 t
18t = 1.5 t^2
1.5 t (t  12) = 0
One answer is t=0. What is the other?