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Acceleration problem. me vs book

  1. Feb 1, 2010 #1
    1. The problem statement, all variables and given/known data
    A bus is traveling at 30.0 km/h speeds up at a constant rate of 3.5 ms/^2. What velocity does it reach at 6.8 seconds later?

    book says 120.km/hour
    I get 115 km/hour

    2. Relevant equations
    Vf=Vi+a x delta t

    3. The attempt at a solution
    First I changed 30.0 km/hour to 30000 m/3600s then reduced to 8.3 m/s. Used formula to get Vf=32.13m/s

    I divide 32.13 by 1000 to get .03213 km/s then 1.9278 km/m then 115.668 km/h.

    I've worked this problem a hundred different ways and get the same answer. AM i right or the book?
  2. jcsd
  3. Feb 1, 2010 #2
    Looks like you and the book are correct. I would assume that the book is answering the question to 2 significant figures, thus 115.668km/h is 120km/h assuming your math is correct.
  4. Feb 1, 2010 #3
    oh my goodness i forgot all about sig figs. Thank you very much
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