Ok, I have a pretty dumb question. A motorcycle cop starts to accelerate with a constant acceleration, a , at the same time a car goes by with a constant velocity, Vcar, find what time it takes to reach the car, the distence, etc. Now, I figured it out as it was a pretty easy problem but I dont understand why it wont work in relative motion as follows: The cop has an initial velocity of -Vcar and accelerates with his acceleration a untill he reaches a velocity of 0. I put it into 0 = Vo + at but that doesnt give me the right answer, so im sure my logic of relative motion is just wrong and am wondering why? Thanks for any help, im sure I am just not thinking of something super easy.