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Homework Help: Simple wattage of the star

  1. Sep 26, 2010 #1
    1. The problem statement, all variables and given/known data
    A) How many W does 1 kg of the sun’s interior produce via nuclear reactions, on average? Compare the sun with a carbattery, which typically produces 190 W/kg. Which body wins?

    B) Estimating the time the two objects are providing their respective power, compare the energy in kWh that 1kg of the two objects emit over their lifetime (one discharge time in case of the battery). Which object wins thiscompetition?

    C) Assuming that the total radiated energy remains the same (it depends on the initial amount of hydrogen that willeventually convert to helium), what would be the main-sequence lifetime of the sun if it produced as much wattageper unit mass as the battery? Would life on Earth exist then? Would life anywhere else in the solar system exist?

    2. Relevant equations

    not sure

    3. The attempt at a solution
    for part i A) did solar luminosity/solarmass=0.2millwatt/kg so for 1kg is 0.2milliwatt and for care batt is 190w...so car wins...

    for part B) not sure what to do hints would be great.. im not under standing it...
    EDIT: or can someone explain the part B cuz im not under standing it.!

    part C) i can do after part B..
    Last edited: Sep 26, 2010
  2. jcsd
  3. Sep 26, 2010 #2
  4. Sep 26, 2010 #3
    kinda urgent. im not understanding what the question B is asking since i dont know thw life times
  5. Sep 27, 2010 #4
    hints are welcomed
  6. Sep 27, 2010 #5
    kWh is another way to say Joules, or energy.
    Expected lifetime of a car battery at 50% duty cycle... 3 years to be optimist.
    Expected lifetime of the sun.... let's say 5 billions years.
    Convert the two times in hours, then multiply by the respective power emitted per kilogram.

    Part B is just that, the asker wants to know how much is the total energy the two systems can give over their entire lifetime.

    How did you get the solar W/kg ?
  7. Sep 27, 2010 #6
    solar luminosity/solar mass = W/Kg

    P.S thank you Quinzio.

    Last edited: Sep 27, 2010
  8. Sep 27, 2010 #7
    hey.. could someone hint me in part C

    for part c can i assume that i can use E=mc^2
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