An object starts at time t = 0 with a velocity of v = +4 m/s and undergoes a constant acceleration of a = -15 m/s2 At what time does the speed of the object reach zero? so, vf = vi + a t so delta t = 0 - 4 / -15 = .27 seconds apparentrly this is wrong answer, but I cant see why? seems really simple! I am suspecting that this question had a typo in it? Sorry, please disregard, it was sig dig problem should be .267 seconds!