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Homework Help: Math questions

  1. Mar 5, 2010 #1
    Can anyone give me the formula or equation so I can solve each of these?

    1. The problem statement, all variables and given/known data
    Question #1
    Suppose the Sun is located 7.4 kiloparsecs from the center of the Milky Way galaxy, and that it orbits the galaxy at a velocity of 240 km/sec. Estimate the mass of the galaxy interior to the Sun's orbit, converted to solar masses.


    Question #2
    A new distant galaxy is discovered which shows a redshift corresponding to a recession velocity of 4429.0 kilometers/second. Using Hubble's Law, and a value of H = 72 km/s per Mpc, what is the distance to the new galaxy in megaparsecs?


    Question #3
    Find the invariant spacetime interval for a particle that travels sideways (in the x-direction only) a distance of 1000 kilometers in 0.1 seconds.


    Question #4
    What is the Schwartzschild radius of a typical stellar remnant black hole with a mass of 18.57 solar masses?


    Question #5
    What is the time required for a black hole with a mass of 5.13 x 1029 kilograms to evaporate by Hawking Radiation?


    Question #6
    What is the temperature of a typical stellar remnant black hole with a mass of 16.32 solar masses?


    2. Relevant equations

    I dont know the formula to solve them.

    3. The attempt at a solution

    I cant do any attempts yet because I dont have the formulas.
  2. jcsd
  3. Mar 6, 2010 #2


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    Science Advisor
    Homework Helper

    Well, you could start by making an attempt to locate the formulas you need in your text book or class notes.

    For the first one, you could use the approximation which says that for the orbit to be stable and circular, the centripetal force needs to be equal to the gravitational force. Find the formulas for those and equate them.

    For the next questions, all you need to do is look up Hubble's law, the formula for spacetime interval, Schwarzschild radius, and so on.

    Certainly your professor doesn't expect you to figure this out all by yourself... don't you have a text book?
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