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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

    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...
  5. 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)
  6. 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.
  7. R

    Rocket Calculations

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

    Find magnitude, help

    It is indeed.
  9. 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
  10. R

    How much heat needed?

    You should end up with 3 separate values for Q which you will have to add up.
  11. 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.
  12. R

    Minimum height of bag?

    Oh, of course. Thanks for that, gneill.
  13. 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).
  14. 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..?
  15. 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.
  16. 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...
  17. R

    Frictional force of car homework

    I can't see where you are going wrong..
  18. 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. :)
  19. 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.
  20. R

    Gauge pressure at the bottom?

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

    Gauge pressure at the bottom?

    They are indeed correct.
  22. R

    What is the mass of this object?

    200/1.2 does not equal 199. The answer should indeed be about 170kg. Check your calculations again.
  23. R

    Momentum, Energy, and Spring problem

    Oh yeah, I made a mistake. I'll look into it.
  24. R

    Momentum, Energy, and Spring problem

    I get x=6.97cm. But you said it should be 5.97cm, right?
  25. R

    Thermodynamics: Internal Energy of a Gas

    My power is 283.48W, which gives t=32.8 s.
  26. R

    Thermodynamics: Internal Energy of a Gas

    Do you know how power and energy are related to each other? Or, more simply, what is power?
  27. R

    Thermodynamics: Internal Energy of a Gas

    Use PV = nRT and U = 3/2nRT therefore U=3/2(PV). R.
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