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Homework Help: Speed of coin

  1. Sep 27, 2013 #1
    1. The problem statement, all variables and given/known data
    A coin slides down a ramp angled at 30∘ with respect to the horizontal. If the coin starts from rest, what is its speed in m/s after sliding 1 m?

    2. Relevant equations
    The acceleration of an object on a ramp is a=mg*sin(x), where g=9.8 m/s^2 and x is the angle.

    3. The attempt at a solution
    I know that the acceleration of the coin is 4.9 m/s^2. that means that in the first second it will be travelling at 4.9 m/s, the second second will be 9.8 m/s, then third second 14.7 m/s, etc. However I don't know how to calculate the speed when the time is not an integer. For example, what is the speed of the coin after 2.3 seconds?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 27, 2013 #2
    See if the equation v = 4.9 t is consistent with your calculations. What if t is not an integer? Can the equation still be used?
  4. Sep 27, 2013 #3
    So what you're saying is that the speed of the object is equal to gt, where g is the acceleration and t is the time displacement. Hmmm... makes sense; the units agree and everything. Why didn't I think of that before?
    So how do I know when the coin has slid 1 meter? Seems like a calculus problem upon inspection.
    Last edited: Sep 27, 2013
  5. Sep 27, 2013 #4
    It is a calculus problem.
  6. Sep 27, 2013 #5
    So how would you recommend doing it as a beginner?
  7. Sep 27, 2013 #6
    From your profile, I see your favorite area is calculus. If you don't want to use calculus, I guess you can use the formulas:

    v = v0+at

    d = d0+v0t+at2/2
  8. Sep 27, 2013 #7


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    Homework Helper
    Gold Member

    By now, you should have become familiar with the kinematic equations for uniform acceleration. You already solved for the acceleration, you are given the distance, it starts from rest, and you want to find its speed after travelling that distance. See


    For the record, you responded
    You mean to say v = at, not v = gt.
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