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  1. R

    Density Parameters using Mathematica

    I'm supposed to solve for re for different values of the omegas. so say 0.2, 0.8; 0.5, 0.5 and so on. And the omegas are constant.
  2. R

    Density Parameters using Mathematica

    Ok, thanks for your suggestion. Right, I need to solve equations (1) and (3) for two omegas only. That is, two of the omegas would be zero, whilst the other non-zero. And the sum of the omegas must always be 1. What I've written so far in Mathematica is: sol = NSolve[r2[z] ==...
  3. R

    Density Parameters using Mathematica

    Homework Statement hello, I have to solve a couple of equations on Mathematica for a project, and since they are not really working out, I wondered if you could help me out a bit. I need to solve equation (1) (you can find the equations in the .doc attached) and plot the solution for a...
  4. R

    Probability of neutrino-electron scattering

    Yeah, that's what I thought, but I am confused about how to find the total probability. An integral or what?
  5. R

    Probability of neutrino-electron scattering

    Homework Statement Ok, I'm given a formula for the cross section of the scattering and I've been told that the detector is a column of water of depth 10m. I need to find the probability of the scattering within the detector. Homework Equations σ = E(in MeV) x 1.5x10-44 cm2 The...
  6. R

    Integrating an equation with scale factor

    Homework Statement Ok, the problem is simple enough, I think. I just think I'm missing something obvious. I have an equation involving the scale factor R(t) and need to integrate it. I am at the first equation and need to get to the second by integrating (with respect of R, I suppose)...
  7. R

    Expectation values

    The integral is just the definition of <p>. p and <p> are not the same thing, so you can't use the formula for p to find <p>.
  8. R

    Expectation values

    because if you use <p> = m d<x>/dt, you would determine the expectation value of the momentum via that of x. But <p> is given only by ∫u p u* dx - it's a definition.
  9. R

    Thermodynamics: Carnot Engine, WHY IS Qhot NEGATIVE?

    From U=Q+W U + -> Internal energy gained by system U - -> Internal energy lost by system Q + -> Heat entering the system Q - -> Heat leaving the system W + -> Work done on the system W - -> Work done by the system R.
  10. R

    Parity in quantum mechanics

    parity is something very simple. If you have an object (or curve, equation..) in x, y, z, let x-> -x, y-> -y, z-> -z. If the body (or equation or curve) looks exactly the same as before, then parity is conserved. Otherwise, it is violated. R.
  11. R

    Spring system with oscillation: two different displacements

    Ah, of course. You do need to use energy conservation, but I told you the wrong thing. total energy of system = potential energy + kinetic energy 1/2 k \Deltax2 = mgx + 1/2mv2 However, the velocity is maximum when the potential energy is 0. (\Deltax is the displacement, x is the position...
  12. R

    Spring system with oscillation: two different displacements

    do you know what the answer should be?
  13. R

    Spring system with oscillation: two different displacements

    It's you again :P I recognised your "delta" ! For part a), how about using energies? Set the initial potential energy, with h=\Deltaxextra and let mgh=1/2 mv2. R.
  14. R

    Spring system with oscillation

    Glad to be of help :) Thanks, have a great day yourself! R.
  15. R

    2nd and 3rd Newton Law Problem

    Because there is friction between the 2kg and 3kg masses. (with a specific coefficient of friction that was given in the question).
  16. R

    Spring system with oscillation

    You are absolutely, right. I beg your pardon. However, my answer for m is completely different from yours. I get m = 738kg. Try solving again the second equation. I would suggest you to square both sides so to get rid of the square root, if you hadn't done so already. R.
  17. R

    2nd and 3rd Newton Law Problem

    c) doesn't require calculations, as it specifically asks to write the answer in symbols only. Part d) is entirely down to tensions, weights and coefficient of friction. For a start, think about what would actually happen when the bodies start moving. it should be easy enough to extrapolate the...
  18. R

    Spring system with oscillation

    use k\Deltax = mg to find k. To do this, use the information given when the car is at rest. So m=120kg, \Deltax = 7.36cm . Once you found k, plug the value in the other equation ( T = 2\pi ...) to find m. R.
  19. R

    2nd and 3rd Newton Law Problem

    what part(s) can't you do? R.
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