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Homework Help: 2-dimentional movement of a point

  1. Nov 2, 2009 #1
    Ok, I know this post is not up to specs but the real problem with this is my trouble with calculus and derivatives (I'm actually worse at that than at English ;) ) in general. I only need help with this step of the homework (basic math help).

    This describes the movement of the point:
    x= 4*x0*cos (Angular velocity*time)
    y= x0*sin (2*angular velocity*time)

    Angular velocity is given as is x0.

    At first I just thought dx/dt = v, and went for it by using the rule (dsink*k/dx=k*cos(k*x)) got:

    Vx=-4x0*angular velocity* sin (angular velocity*t)
    Vy=x0*2*angular velocity*cos (2*angular velocity*t)

    I know this is wrong. Since I realised as soon as I wrote it that, angular velocity is v/r so d(v/r)/dt, trying to get throught that using the rule for d(f(x)/g(x))/dx it got quickly complicated since looking at the XY graph (I got something that looks like a 8) for movment leads me to belive r is not constant.

    Anyway the more basic problem is that I don't know how to solve sin (f(x)*x)/dx or the second one for cos :(

    I can solve d(f(x)*x)/dx and dsin(x)/dx (since both are covered by the simple equations) but putting them together confuses the heck out of me.

    You guys where very patient and helpful with my previous problem, I hope I can learn from you again. :) Again, thaks for taking the time to help a newbie with something (for you) this trivial. :)

    PS I hope angular velocity is the proper english word the derivative for what I mean is dAngle/dTime its related to velocity (v= r * angular velocity).
  2. jcsd
  3. Nov 2, 2009 #2


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    It is not wrong. You took the derivatives correctly so the velocity components are what they are. Here you do not have circular motion, so ω=v/r does not apply. If you had circular motion then

    x2+y2 = constant. This is not the case here.
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