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!

Homework Help: Schwarzschild Radius

  1. Apr 2, 2009 #1
    A black hole is an object so heavy that neither
    matter nor even light can escape the influence
    of its gravitational field. Since no light can
    escape from it, it appears black. Suppose a
    mass approximately the size of the Earth’s
    mass 7.22 × 1024 kg is packed into a small
    uniform sphere of radius r.
    The speed of light c = 2.99792 × 108 m/s .
    The universal gravitational constant G =
    6.67259 × 10−11 Nm2/kg2 .
    Hint: The escape speed must be the speed
    of light.
    Based on Newtonian mechanics, determine
    the limiting radius r0 when this mass (approx-
    imately the size of the Earth’s mass) becomes
    a black hole. Answer in units of m.


    Where the V[e]is the speed of light.

    This should be easy but apparently i am getting it wrong some how... any ideas?
  2. jcsd
  3. Apr 3, 2009 #2


    User Avatar

    Well, your equation is slightly wrong. It is a simple matter of plugging and chugging, but your equation should be V=sqrt(2GM/r)
  4. Apr 3, 2009 #3


    User Avatar
    Homework Helper

    John Michell, c1783, 133 years before Schwarzschild.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook