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Inclined Planes

  1. Nov 25, 2006 #1
    I am doing my Science Fair project on Inclined Planes. My experiment mainly revolves around the ANGLE of the inclined plane determining the TIME it takes a ball to roll down the plane. I was wondering it I kept all of the other variables the same (length of the plane, weight of the ball) and only manipulated the angle of the plane, what the equation would be used to predict the time. I researched all that I could in books and online but everything I found gave me all of these complex equations that didn't have to do with angle (or at least I think they didn't). Any help would be appreciated, thanks!
  2. jcsd
  3. Nov 25, 2006 #2


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    If I understood, you are trying to find a function t(A), where A is the angle of the incline. Well, you can use energy conservation to find the velocity of the object on the bottom of the incline, expressed in terms of A. Further on, you should plug that velocity into the kinematic equation of velocity of the object, which is v(t) = g*sinA*t. You can now easily express the time t as a function of the angle A. I hope that helped.
  4. Nov 26, 2006 #3
    So basically this means find velocity right? Why do I have to find the velocity when it's at the bottom of the incline (aka the end of it). How do I use energy conservation to find it? Sorry if my questions irritate you because I;m still really new to physics =(
  5. Nov 26, 2006 #4


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    Use the fact that the potential energy of the object at the top of the incline equals the kinetic energy at the bottom (since kinetic energy at the top equals zero, as does potential energy at the bottom). You can find the velocity from this equation.
  6. Nov 26, 2006 #5
    You could also avoid energy all together and use d=1/2at^2. The acceleration is still gsinA. So time would be sqrt(2d/gsinA). Youll come up with the same thing either way, except this formula depends on the length of the ramp, not the vertical height. If youre angle is changing, your height will be changing too, so this is probably better than energy
  7. Nov 26, 2006 #6
    would using these formulas work and are they correct?:

    distance = .5* A * T^2 or rearranged as t= square root of (distance/.5*A)


    mass*gravity*Sin of the angle - friction = mass*acceleration

    I can use the second one to find the acceleration because I am given the mass and can solve for the sin of the angle, and then plug it into the first one and then solve for time?
  8. Nov 27, 2006 #7


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    You didn't mention anything about friction. But if you are given a frictional force/coefficient of kinetic friction, you can use the second one to find the acceleration. The method turdferguson suggested should work just fine, too, if you're not given any frictional force.
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