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  1. J

    Desperate for astrophysics help

    The energy generation rate for p-p fusion has an approximate dependence on density and temperature given by: E= e (p/pc)(T/Tc)^4 i don't know how to write all the symbols so in the above: E is epsilon, e is epsilon at the centre of the star, p is the density, pc is density at the centre...
  2. J

    Spectra Troubles

    Consider the Lyman photons for Hydrogen-like atoms with Z greater than one. Which of these atoms have Lyman alpha photons in the 1)visible 2)UV 3)X-ray and 4)gamma-ray parts of the spectrum? Can list ranges of values of Z in the answers. My thoughts are to use 1/lambda=...
  3. J

    Absolute zero founder

    This is a pretty straight forward question. Does anyone know who exactly first determined the value of absolute zero and when it was. I am getting conflicting information about it. this is not a question i have to answer, just a little bit of information i would like to include in a physics...
  4. J

    Astrophysics - Can there be a contact binary from white dwarfs

    Question: A typical white dwarf has a mass of 1 solar mass and a radius of 10 thousand km. A typical neutron star has a mass of 1.5 solar masses and a radius of 30km. Given that there's a natural speed limit in Nature, namely the speed of light, is it possible to have a contact binary...
  5. J

    Integral help

    this should be easy, but i'm struggling. i'm trying to help a friend solve: integral(5x^3(1+x^2)^1/2), sorry i don't know how to do the integral sign. i did a u sub with u=1+x^2, du=2xdx and u-1=x^2 so: (5/2)integral((u-1)(u)^1/2) i get (1+x^2)^5/2-10/6(1+x^2)^3/2 +C the...
  6. J

    Theory question

    i have a question where it asks me to find the uncertainty in a ball's postion (m=50g). i have that part all figured out, but then it asks me what the answer indicates about the relevance of quantum mechanics to macroscopic objects. (the answer was approx. 10^-32m, a very small uncertainty)...
  7. J

    Double slit electron experiment

    A monochromated beam of neutrons (speed 0.40 m/s) is directed through a double slit with 1.0 mm separation. An array of detectors is placed 10m from the slit. a)what is the de Broglie wavelength of the neutrons? b)how far off-axis is the first zero-intensity point on the detector array...
  8. J

    Physics HUP help

    A ball of mass 50g moves with a speed of 30 m/s. If its speed is measured to an accuracy of 0.1%, what is the minimum uncertainty in its position? What does this answer indicate about the relevance of quantum mechanics to macroscopic objects? I am completely confused. My prof just gave us...
  9. J

    Parametric equations for particle motion

    Describe the motion of the particle with position (x,y) as t varies over the given interval. x=2+cost y=3+sint where t is greater than or equal to 0 and less than or equal to 2 pi i've tried to eliminate t and came up with y=3+sin(arccos(x-2)) i don't know if...
  10. J

    Power series

    Evaluate the indefinite integral as a power series and find radius of convergence. (i don't know how to type the integral and summations signs, sorry) (integral sign) (x-tan^-1x)/x^3 dx. ( if you write this out it makes more sense) i was able to find the power series of tan^-1x =...
  11. J

    Power series representations

    Evaluate the indefinite integral as a power series and find radius of convergence. (i don't know how to type the integral and summations signs, sorry) (integral sign) (x-tan^-1x)/x^3 dx. ( if you write this out it makes more sense) i was able to find the power series of tan^-1x =...
  12. J

    Leslie Cube (still)

    sorry, this was my question from yesturday, and now my assignment is due tomorrow. anyone have any help for me? A Leslie cube has a surface temp of 97C. One of its four side faces has an area of 100 cm^2 and is painted black. Calculate: a) the wavelength at which the spectral intensity...
  13. J

    Leslie Cube

    A Leslie cube has a surface temp of 97C. One of its four side faces has an area of 100 cm^2 and is painted black. Calculate: a) the wavelength at which the spectral intensity (per unit wavelength) is a maximum b)the total intensity (all wavelengths) of the emitted radiation just outside...
  14. J

    Electron volts

    The photocurrent of a photocell is cut off by a retarding potential of 2.92V for radiation of wavelength 250nm. What is the work function of the photoemitter? I want to use the equation: PHI=hc/lambda-Ve, where V is the stopping voltage (sorrry I don't know how to do the Greek letters for...
  15. J

    Real vs Carnot

    Homework question: A 20% efficient real engine is used to speed up a train from rest to 5.00m/s. It is known that an ideal (Carnot) engine having the same cold and hot reservoirs would accelerate the same train from rest to 6.50m/s using the same amount of fuel. Assuming that the engines...
  16. J

    Internal Energy

    I have a question concerning internal energy and the First Law of Thermodynamics. If you plotted P vs V and the shape of the graph is an enclosed shape ie) square or triangle, would the total internal energy in one cycle be zero? (one cycle is for example-start at top left of square and finish...
  17. J

    Number of oxygen molecules

    i have a multi-part question which is fine except for two areas. 1) how many oxygen molecules travelling at this speed (i already have the speed calculated) are necessary to produce an average pressure of 1.00 atm? 2) calculate the number of oxygen molecules that are actually contained...
  18. J

    At what value of h does the flow stop?

    I am new here so I hope that someone may have some advice. I am having trouble with a homework question which is quite lengthy. -- A large tank of water has a hose connected to it as shown in the figure. The tank is sealed at the top and has compressed air between the water surface and the...
  19. J

    What is the speed with which the water flows out of the hose

    I am new here so I hope that someone may have some advice. I am having trouble with a homework question which is quite lengthy. -- A large tank of water has a hose connected to it as shown in the figure. The tank is sealed at the top and has compressed air between the water surface and the...
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