1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Elevator going up with constant velocity but changing acceleration

  1. Jan 29, 2014 #1
    1. The problem statement, all variables and given/known data
    An elevator goes up 180 m by first accelerating at a constant rate of 1.0 m/s2, then staying at a constant
    speed of 9 m/s and then decelerating at a constant rate of -­‐‑1.0 m/s2. How much time does it take the
    elevator to go from bottom to top?

    so i know that d = 180m
    a = 1.0 m/ssfor the first part
    v = 9 m/s
    and for the last part a = -1 m/ss


    2. Relevant equations

    Im not sure which kinematics to use, there are two that I tried using

    d=vit + 1/2at2

    and

    vf = vi + at



    3. The attempt at a solution

    I tried to find the time for the part where the elevator is accelerating by doing

    9 = 0 + 1t

    so t = 9s

    then I tried to find the distance for which the elevator was going up by doing

    d = 0(9) + 1/2(1)(92) and got d = 40.5

    so then the d for when its decelerating is 139.5 which i plugged into

    d=vit + 1/2at2

    and tried to solve for t but i ended up getting a weird answer with a square root.


    am i approaching the problem the right way? or am i completely wrong?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jan 29, 2014 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    correct so far...

    It also travels some distance with constant velocity...


    ehild
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Elevator going up with constant velocity but changing acceleration
Loading...