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Solving circular motion problem

  1. Oct 20, 2016 #1
    1. The problem statement, all variables and given/known data

    Our teacher gave us a formula to solve it by creating a computer program but the problem is i'm not good at physics. I need to know what is Fc,Mr,Fk etc..

    1.) Fc = Mr(theta - Oo) ^ 2 / (t - tn) ^ 2

    2.) M = Fk / Mk(m)(g)cos(theta)

    2. Relevant equations

    3. The attempt at a solution
    I tried to google my formula but end up nothing so i registered here.

    I already created the computer program to solve it i just assigned a value for them but i need to know what am i solving for, e.g r is the radius, m is the mass
  2. jcsd
  3. Oct 20, 2016 #2


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    Staff: Mentor

    Welcome to the PF. :smile:

    Please post the exact problem statement. As you have written it out so far, we would just be guessing. Also, I've changed your thread title to be more descriptive of the problem you are asking about. Please try to use very descriptive thread titles here. Thanks.
  4. Oct 20, 2016 #3


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    In principle, you do not need to have any idea what the variables represent in order to write a program to solve an equation. But you do need to know which are the inputs and which are the unknowns to be calculated.
    From your post, it is not entirely clear to me how many variables there are. E.g. is Mr one variable or the product of two variables, M and r? I suspect the statement of the problem given to you makes that clear, but it has been lost in the way you have typed it out. Please use subscripts and superscripts as appropriate (use the X2 and X2 buttons in the toolbar).
    The Oo looks rather unlikely. Is this perhaps a Greek character? You can get theta etc. and some special symbols from the ∑ button in the toolbar.
  5. Oct 20, 2016 #4
    1.) Fc = Mr( - 00)2 / (t - tn)2

    in number 1 it's solving for Fc <- i dont know what is Fc

    2.) m = Fk / Mk(m)(g)cos(theta)

    in number 2 it's solving for m

    i can't find a symbol for a theta, but this is the closest symbol for theta: ∅
  6. Oct 20, 2016 #5


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    Why do you care? If you are given inputs Mr, 00 (or do you mean O0?), t and tn, it seems simple to calculate Fc. I have the feeling you have not fully explained your task.
    Is the equation m = Fk / (Mk(m)(g)cos(theta))? And does "Mk(m)" mean Mk multiplied by m or that Mk is a function of m? If it means multiplied by, you need to rework the equation so that m only appears on one side.
  7. Oct 20, 2016 #6
    No Mk(m) means multiply and it's not a function of m

    and what is Fc is it force? and what is m in number 2? is it mass?
  8. Oct 20, 2016 #7


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    There is no way anyone on the Forum can tell for sure, we can only guess.
    Fc is sometimes used for centripetal force. If so, I can try to make sense of the rest of the equation, which you originally posted as:
    You later put that r as a subscript, but I suspect that was wrong. It's probably a radius.
    The Oo could be θ0, an initial angle. The tn maybe t0, an initial time. That gives us
    That makes sense if a (small) object mass M is rotating at distance r from an axis at constant speed and moves from an angular position θ0 at time t0 to θ at time t. The formula would give the centripetal force required.
    Almost surely.
    You originally posted this as
    When you put in subscripts you changed it to
    which resulted in the variable m appearing on both sides. I now assume you mean either ##M = \frac{F_k}{M_kmg\cos(\theta)}## or ##M = \frac{F_k}{M_k}mg\cos(\theta)##. Neither makes obvious sense. Fk smells like a force, maybe of kinetic friction. mg cos(θ) would also be a force. Not sure what M and Mk are supposed to be, but one would guess they are of the same type.
    If ##M = \frac{F_k}{M_kmg\cos(\theta)}## then ##M M_k= \frac{F_k}{mg\cos(\theta)}##, making the M's dimensionless.
    If ##M = \frac{F_k}{M_k}mg\cos(\theta)## then ##M M_k= F_kmg\cos(\theta)##, making the Ms also forces.
  9. Oct 20, 2016 #8

    Thank you sir!!! and that explains my problem!!
    Kinetic Friction and Centripetal Force is what i need. Thanks a lot!
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