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!

Help With finding displacement in uniform acceleration

  1. Sep 27, 2013 #1
    1. The problem statement, all variables and given/known data

    A subway train starting from rest leaves a station with a constant acceleration. At the
    end of 7.8 s, it is moving at 11.778 m/s. What is the train’s displacement in the first 5.6394 s of motion? Answer in units of m


    2. Relevant equations

    a= velocity final - velocity initial / time

    delta x = velocity initial(time) + 1/2 (a)(t)^2


    3. The attempt at a solution

    delta x = 0 (7.8)+ 1/2 (1.51)(7.8)^2
    delta x = 1/2 91.8684
    delta x = 45.9342
    that is delta x for 7.8 seconds. how do i find delta x for 5.6394 seconds?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 27, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Use the same formula, but with the different time! (Why did you solve for x at t = 7.8 second?)
     
  4. Sep 27, 2013 #3
    i also did substitute 5.6394 s for the time rather than 7.8 seconds, and i got 66.4208532002 for delta x. but this was wrong. what did i do wrong?
     
  5. Sep 27, 2013 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Show your calculation. (You know you must have done something wrong. This displacement is bigger than the one you found for the longer time. That can't be right.)
     
  6. Sep 27, 2013 #5
    delta x = 1/2 (1.51)(5.6394)^2
    delta x = 24.0111384

    that is what i got this time.....
     
  7. Sep 27, 2013 #6

    Doc Al

    User Avatar

    Staff: Mentor

    That's more like it.
     
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: Help With finding displacement in uniform acceleration
Loading...