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Help me with this uniform accelration problem

  1. May 31, 2007 #1
    I'm learning physics and I'm now working on with one line motion problems and I'm jammed with this one problem:

    A ball starts from rest and rolls down a hill with uniform accelration, traveling 150m during the second 5.0s of it's motion. How far did it roll during the first 5.0s of motion?

    I just can't figure out how to solve this. Could someone help me?

    Thanks!
     
  2. jcsd
  3. May 31, 2007 #2
    This sounds like a homework question.

    Anyway:
    http://www.physchem.co.za/Graphs/Equations.htm
    The 4 Basic linear Equations of Motion can help.

    Hint:
    -Use s=ut+(at^2)/2 & v=u+at
    -Find a
    Then use s=ut+(at^2)/2

    If you need more help post at the Homework Questions section.
     
  4. May 31, 2007 #3
    Yeah, I have tried those equations, but I can't get the right answer...
     
    Last edited: May 31, 2007
  5. May 31, 2007 #4
    Please post how you worked out the problem, so that we may point out the errors.
     
  6. May 31, 2007 #5
    Well, I'll try :) So ball starts from rest, so Xo = 0, Vox = 0, T1 = 0. Then the ball rolls 5s and it's place is X1 and V1x = ?. Finally the ball rolls the second 5s and then X2 = X1 + 150m, V2x = ? and T2 = 10s


    When the ball rolls first 5s:
    (1) X1 = 1/2(AxT1^2)

    The ball rolls second 5s (from X1 to X2):
    (2) X2 = X1 + V1xt + 1/2(AxT2^2)

    Then I combine those equations (1) and (2), but with no luck.
     
  7. May 31, 2007 #6
    You should also write V1 in terms of the acceleration A.
    Eliminate all other unknowns except A, remember you have values for X2, T1 and T2.
     
  8. May 31, 2007 #7
    Correct me if I may be wrong.:smile:

    df=distance in first 5s
    t=5 in all cases

    df=ut+(at^2)/2
    since: v=u+at
    therefore:df=(0+at)t+(25a)/2
    therefore:150=37.5a
     
    Last edited by a moderator: May 31, 2007
  9. Jun 1, 2007 #8
    Yes, you are correct and I hope the OP has understood the solution.
     
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