1. Apr 2, 2009

### xRandomx210

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
Use:
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.

V[e]=Sqrt(2GM)(r))

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. Apr 3, 2009

### cjl

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

3. Apr 3, 2009

### turin

John Michell, c1783, 133 years before Schwarzschild.