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Not quite understanding m/s^2

  1. Jul 12, 2011 #1
    1. The problem statement, all variables and given/known data

    Suppose a car starts from rest. The car accelerates straight
    down the road and and at t =30 seconds, attains a speed of
    v=30 km/h. Determine the average acceleration of the car.

    2. Relevant equations


    3. The attempt at a solution

    so the answer is 1000m / hr /s2....
    now the textbook wants you to convert it fully into m/s2. what would i do next
  2. jcsd
  3. Jul 12, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    No, that would be 1000 m/hr/s.

    But better to start by converting the speed from km/h to m/s and redoing the calculation. How many seconds in an hour?
  4. Jul 12, 2011 #3


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    Convert hours to seconds. I'd have converted 30km/hr to m/s before starting the problem.

    You still need to do it by hand to learn it, but when doing such calculations lately I use http://futureboy.us/frinkdocs/" [Broken], which can cope with any units automatically. (It also has a web and a smartphone interface. Just be sure to use lots of parentheses, especially in denominators, as 10m/30s =1/3m*s, while 10m/(30s) = 1/3m/s.) It can cope with virtually any units from Irish cubits to crocodiles, and has many cool features that make it easy to use. It's also great for checking your work.

    the problem is equivalent to (30km/hr)/(30s) = (30(1000m)/(3600s))/(30s) = (25/3 m/s)/(30s).
    Last edited by a moderator: May 5, 2017
  5. Jul 12, 2011 #4
    If you want to be quick in calculations the i will suggest you to stop using calculators and do calculations by hand.

    and Doc AL is right ... you problem is just that you need to convert units before you start with the solution ... you can also do it in the end but its easier to do it in beginning.
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