- #1

RK1992

- 89

- 0

KE = GPE

0.5mv² = GMm/r

r=2GM/v²

and then if the escape velocity is the speed of light, then the radius of the region of space where you can't escape is given by r=2GM/c²

but the equation KE=0.5mv² is just valid for small values of v and can be obtained from the expansion of m(γ-1)c²... m(γ-1)c² is not defined for v=c, though, so why does the maths turn out nicely when its so clearly wrong to use KE=0.5mv²?

thanks :)