1. Not finding help here? Sign up for a free 30min 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!

Introductory kinematics word problem

  1. Jul 4, 2009 #1
    1. The problem statement, all variables and given/known data

    A competitor is aiming to complete a 1500m wheel-chair race in less than 4.0 minutes. After moving at a constant speed for exactly 3.5 minutes, there were still 240m to go. What must his acceleration before the remaining distance if he were to finish the race on time?

    Given:
    d1= 1260m [forward]
    d2= 240m [forward]
    t1= 210s
    t2= 30s

    Required: v1, v2 possibly?, and a


    2. Relevant equations

    v1 = d/t
    and d = v1*(t+a(t)^2)/2 ?

    3. The attempt at a solution

    v1=1260m/210s
    v1=6m/s

    d = v1*(t+a(t)^2)/2
    a= (2d/t^2)-v1*t
    a= (2*240m/30s^2) - 6m/s*30s
    a= something horribly incorrect

    the answer at the back of the book is 0.13m/s^2. im guessing that im not approaching the second part of the question correctly. i tried it again with an equation using v2, but im still getting weird answers.

    help please !

    also, im sorry i dont know how to use latex :/
     
  2. jcsd
  3. Jul 4, 2009 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi shaools! Welcome to PF! :smile:

    (don't bother about LaTeX for something like this … the SUB and SUP tags are fine, and they save a bit of server space also! :wink:)
    hmm … you're messy with brackets, which leads you to make mistakes

    that middle line is wrong. :smile:
     
  4. Jul 4, 2009 #3
    wow.

    i managed to screw up the initial equation twice in that post. there's no way to edit posts is there?

    i meant to post this equation for displacement and acceleration:

    http://id.mind.net/~zona/mstm/physics/mechanics/kinematics/EquationsForAcceleratedMotion/Origins/Displacement/Image78.gif" [Broken]

    soo...

    d = v1*t + (a*t^2)/2
    a = 2d/(t^2) - v1*t

    and then when i plug my values in, i get funky answers.
    i think i might just be using the wrong equation, or i might be plugging in incorrect values. im really not sure.

    thank you for checking tho!
     
    Last edited by a moderator: May 4, 2017
  5. Jul 4, 2009 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Nope … still wrong :redface:

    Write it out step by step … don't try to do any of it in your head!
     
  6. Jul 4, 2009 #5
    ah, bested by bedmas

    lol let me attempt this once more...

    a= [2(d - vt)]/ t^2 ?
     
  7. Jul 4, 2009 #6
    a = [2(240m - 6m/s*30s)] / 30^2
    a = 0.13m/s^2

    yup :).

    thank you mr. fish !
     
  8. Jul 4, 2009 #7

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    :tongue2: blubblelubbleglubblelubblephlrrrrrrp! :tongue2:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Introductory kinematics word problem
  1. Kinematic word problem (Replies: 2)

  2. Word problem (Replies: 6)

Loading...