Bob N

I was thinking the halfway point, but that leads me to another wrong answer. I can't see any other interesting points where that would happen

I'm doing this question for physics, and I'm a bit stuck. The question is: A hotel elevator ascends 200m with maximum speed of 5 m/s. Its acceleration and deceleration both have a magnitude of 1.0 m/s^2 a) How far does the elevator move while accelerating to full speed from rest? b) How long does it take to make the complete trip from bottom to top? Part a I did Vf^2 = Vi^2 +2aΔx 25 = 0 + 2(1)Δx 25/2 = Δx = 12.5 m (and I got the answer right) now part b I tried a couple of ways, I tried separating the problem after 12.5 m, so x(t) = (.5 a t^2) + Vit + Xi 200 = .5t^2 + 5t + 12.5 So quadratic is .5t^2 +5t -187.5 = 0 t = 15 s I added 5 s on top of that, since that is the time to the 12.5 m, from Vf = Vi + a t 5 = 0 + 1(t) but 20 s is apparently the wrong answer. I tried treating the whole problem as one part, like 200 = .5at^2 + Vit + Xi 200 = .5t^2 + 0 + 0 400 = t^2 t=20 s what am I doing wrong?