Recent content by jimz

  1. J

    Particle subject to position dependent force

    "The net work done by all the forces acting on a body equals the change in its kinetic energy." Not seeing it...
  2. J

    Particle subject to position dependent force

    Homework Statement A particle with total energy E and mass m is subject to a force F(x)=\xi x^4. Find the velocity v of the particle as a function of the position x, and sketch a phase diagram for the motion. Homework Equations T=\frac{1}{2}m\dot{x}^2 U=constant F=m\ddot{x} The Attempt at a...
  3. J

    HELP -How many meters does it take for a car to stop?

    Your observation that you do not need time to solve the problem is correct. The observation that all those equations involve time is not- look carefully.
  4. J

    Find the period of oscillation of a bead on a cycloid string

    Still can't see what I did wrong... how does the 4a not become a?
  5. J

    Find the period of oscillation of a bead on a cycloid string

    Thanks! I forgot that dθ/dt is ω and it's the chain rule twice. So close, but why am I off... -\frac{1}{4}\omega^2u+\frac{g}{4a}u=0 \frac{1}{4}\omega^2=\frac{g}{4a} \omega=\sqrt{\frac{g}{a} T=\frac{2\pi}{\omega}=2\pi\sqrt{\frac{a}{g}
  6. J

    Find the period of oscillation of a bead on a cycloid string

    I'm sure that the equation of motion is correct. It's long and uses some tricky trig identities, but more importantly it matches the answer as given. In any event, it's the period of oscillation part I do not understand.
  7. J

    Find the period of oscillation of a bead on a cycloid string

    Homework Statement Find the period of oscillation of a bead on a cycloid string. If it matters, the original equations of the cycloid were x=a(\theta-sin\theta) and y=a(1+cos\theta) Homework Equations This is a small part of a larger problem... I found the equation of motion of a bead on a...
  8. J

    Help understanding derivatives of time; chain rule.

    I'm having a bit of a hiccup understanding the differentiation that I am doing... I'd like to be clear on the concept rather than just knowing 'apply chain rule'. So I have a particle with equation: y=a(1+cos\theta) now the derivative with respect to time (the velocity in y) is...
  9. J

    Incline plane, two masses, a pulley

    yes, it's a problem from our book. Does that matter? I now think I set it up correctly and it's now just a math problem but I still can't get anywhere closer to the solution for theta.
  10. J

    Incline plane, two masses, a pulley

    Homework Statement A string through an ideal pulley connects two blocks, one (mass=2m) is on an inclined plane with angle theta to horizontal and coefficient of kinetic friction mu. The other block (mass=m) hangs off the pulley on the high side of the inclined plane. (looks like this, except...
  11. J

    Help understanding math on inclined plane example

    I'm trying to follow a very simple example example in a text (Marion/Thornton example 2.1) and I think my rusty calculus is tripping me up and I'm just being stupid. I understand how to derive the acceleration down the plane: \ddot{x}=g\sin\Theta but next they say 'we can find the...
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