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Motion: Solving problems using equations

  1. Sep 19, 2009 #1
    Im sorry if this is in the wrong area ! and I know that this is the easiest question in the history of physics but I need help. I think some of the answers in the back of the text are wrong but I might be just the biggest idiot on the face of the earth so feel free to point that out. anyways .....1. The problem statement, all variables and given/known data
    If 100m sprinters accelerate from rest for 3.5 s at 2.8 m/s (squared) , how far have they ran to this point ? How long will it take them to complete the 100m sprint , assuming they maintain their speed the rest of the way ?
    2. Relevant equations

    d= v1t + 1/2a t (squared)

    I think ?

    3. The attempt at a solution

    = 3.5 + 1/2 (2.8)(3.5) squared
    = 3.5 + 1/2 (2.8)(12.3)
    =3.5 + 34.2 divided by 2
    = 3.5 + 17.2
    = 20.7 sorry I don't have the division sign or superscript

    and I can't do the rest of the question without having the first answer correct. The text says the answer is 17 m


    HELP !!! Please help a huge idiot
     
  2. jcsd
  3. Sep 19, 2009 #2

    Doc Al

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    Staff: Mentor

    Hint: What's the initial speed? (What you call v1.)
     
  4. Sep 19, 2009 #3
    Isn't it 0 m/s ? It says from rest
     
  5. Sep 19, 2009 #4

    Doc Al

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    Staff: Mentor

    Exactly! Do you see what's wrong with your calculation now?
     
  6. Sep 19, 2009 #5
    OH wow thats great. I was adding instead of multiplying ! Thanks
     
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