A clump of matter does not need to be extraordinarily dense in order to have an escape velocity greater than the speed of light, as long as its mass is large enough. You can use the formula for the Schwarzschild radius Rs to calculate the volume 4/3piRs^3 inside the event horizon of a black hole of mass M. What does the mass of a black hole need to be in order for its mass divided by its volume to be equal to the density of water (1 g/cm^3) ? So I have the density which = mass/volume = 1 g/cm^3 I know I'm suppose to find the mass but then how do I know what the volume is? If the volume formula is 4/3pir^3, I'm having trouble with finding radius now, since I don't have the volume, I'm really frustrated about this question.Also using Schwarzchild radius formula Rs = 2Gm/c^2 seems useless because I don't have mass now?! Err so I need mass and volume but all I have is density?!