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  1. R

    Rocket Height

    From the moment the fuel finishes, only one force acts upon the rocket: gravity. So find the the velocity the rocket possesses after those 7 seconds of propulsion and then use the constant acceleration formulae to find the height at which the rocket has v=0. R.
  2. R

    A man in an elevator at the forces affecting him

    Just use Newton's Laws to know that a force corresponds to an acceleration. As the elevator moves, a new force is exerted on the man. The direction of this force depends on the direction of motion of the elevator. Does it make sense?
  3. R

    Need help. How do i start the problem, thank you.

    The latent heat is the amount of energy absorbed or emitted by a system during a phase transition (liquid -> solid, say) carried out at constant temperature. You should proceed in calculating what the latent heat is in this instance; then it should be fairly obvious what to do ;) R.
  4. 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.
  5. 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] ==...
  6. 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...
  7. 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?
  8. 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...
  9. 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)...
  10. R

    Constructive or destructive interference- Car radio

    Use c=νλ with the values given for the frequency and the speed of light. (ν here is the greek letter "nu", denoting frequency) From this, you'll find the wavelength of the wave. Now, the waves will "hit" the wall and be reflected towards the car again, so the intereference will be costrunctive...
  11. R

    Angular velocity of an airplane propeller

    yes, it is right. Just maybe don't leave it as 3800pi/60, but compute the actual value. (But i'm sure you were going to do it anyway)
  12. R

    Capacitors in Series

    Because there are two capacitors in the circuit. If you use C=C2 (1e-6), then you are just considering a circuit having *one* capacitor. You basically need to find C to see how the capacitance is split between the two capacitors. That would also give you how the charge is split.
  13. R

    Rocket Calculations

    Just use: p=mv and a=dv/dt (and F=ma, of course).
  14. R

    Find magnitude, help

    It is indeed.
  15. R

    Find magnitude, help

    Just look at how the RHS of the two equations below is altered and you will know how to change the LHS as well. N = kg m/s^2 ? = kg m/s
  16. R

    How much heat needed?

    You should end up with 3 separate values for Q which you will have to add up.
  17. R

    How much heat needed?

    You *also* need to use Q = mL, where m is the mass and L is the heat of fusion/vaporisation. R.
  18. R

    Minimum height of bag?

    Oh, of course. Thanks for that, gneill.
  19. R

    Minimum height of bag?

    I would have guessed g/cm^3 as you did. But purely because the value was close to 1. (The density of water is 1g/cm^3).
  20. R

    Find magnitude, help

    N is kg m/s2, but you only have kg m/s. So you can either leave it as kg m/s or rewrite it as..?
  21. R

    Minimum height of bag?

    It looks correct. But do tell your teacher that NO value should be given without its units. (i'm obviously referring to the "1.04" for the specific gravity.) R.
  22. R

    Find magnitude, help

    Your final value is correct. However, being a magnitude , it should have positive sign. As for the units, just work them out by what you have in the equation. I'm sure you know the units of m and v (and you're given them, anyway), so just use those. Start drawing a diagram showing the...
  23. 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>.
  24. R

    Frictional force of car homework

    I can't see where you are going wrong..
  25. R

    Gauge pressure at the bottom?

    Oh ok, it was down to notation, then. When I thought you might need the atmospheric pressure is because I was calculating P1, but you needed P1-P0. :)
  26. R

    What is the mass of this object?

    they probably meant 170kg. I got 167.8kg, which approximated to two significant figures gives indeed 170kg.
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    Gauge pressure at the bottom?

    Actually, I wonder whether you should also consider atmospheric pressure. Also, why is it P1-P0 and not +?
  28. 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.
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