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A Marble Rolls Around a Circular Cone - Diagram

  1. Sep 24, 2013 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations


    3. The attempt at a solution

    I said that the letter B was the normal force which I derived from just drawing an FBD of the ball on the left side of the code

    For acceleration I used Fnet=mg so the Fnet was gravity, so from there I said that the letter representing normal force was pointing in the same way of fnet, being letter E..

    It was wrong. Please help
  2. jcsd
  3. Sep 24, 2013 #2


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    OK for the normal force direction.

    For the direction of the acceleration, you should be able to see what it is without worrying about the forces. Use what you know about the acceleration of a particle moving in a circle with constant speed.

    [Although you don't need it for this question, the correct formula is Fnet = ma, not Fnet = mg. The acceleration of the particle is not g for this problem. Fnet is the vector sum of all of the forces acting on the particle.]
  4. Sep 24, 2013 #3
    So my answer would be that the acceleration is pointing towards the center of the circle. But that could be C, K, or S. How would I answer this? It has to be one of those but I don't know which.
  5. Sep 24, 2013 #4


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    The question says to pick answers for the acceleration from the choices Q through X.
  6. Sep 24, 2013 #5
    I just attempted BS and was incorrect
  7. Sep 24, 2013 #6


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    Ah. I see an extra thing you have to consider. Sorry, I didn't see that before. Note that the question asks for you to pick the normal force from the choices A-X. Now B, J and R all have the same direction. But they have different magnitudes. So, you will now have to decide which of those has the correct magnitude. For this you will need to use Fnet = ma.

    [HINT: Consider the y-components: ƩFy = may ]
    Last edited: Sep 24, 2013
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