you see MR . Arjun Artro, as far as i can imagine, you can use general relativity and its geometrical picture of our universe to find a solution to your problem.
if you do not know why according to general relativity no light can escape from a black hole, then i'll try to explain it to you. if you take a stretched rubber sheet and put objects of different masses onto its surface , you will see that the heavier the object the more is the curvature of the rubber sheet. now, here we take that the rubber sheet represents the very nature of the space-time in our universe. we all know that a black hole is a mass of infinite density and therefore it will act like an object of infinite 'weight' and thus will form an infinite curve in the rubber membrane(space-time). so when light passes near the curvature of the black hole, it starts to fall within the curve of the black hole. but since it is an infinite curve, then theoretically, we should need infinite energy(impossible) to over come the curve
and leave through the other side. now, think of an object moving with uniform velocity in circular orbit. its direction changes every instant but its velocity does not.
same is the case here. the light travels with constant velocity but when it 'changes its direction towards the infinite depth of the black hole's 'gravity well', the velocity does not change.
hope that helps !