There is a student running at a constant velocity after a stationary bus, when the student is a certain distance from the bus, the bus begins to accelerate. how many seconds does the student have before overtaking the bus. In order to solve the problem I have to combine acceleration formulas for the student and the bus. x + vt - (1/2)gt^2 = x + vt - (1/2)gt^2 and solve for time. This ends up being a quadratic formula so I get two solutions for t. both solutions end up being positive. How do I know which one to use for the correct answer?