1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    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?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Math questions Date
Very basic math question... Sep 17, 2017
Kinematics Mechanics Oct 8, 2016
Another cannonball question Mar 13, 2015
A question about a certain math argument in Griffiths Jan 26, 2015
Train question using velocity Nov 11, 2014