As I have heard that light bends under the gravitational force. While according to formula "w=mg", gravitation acts on objects that have mass, but light has no mass if it is considered as photon nature. And also if light bends under gravitational FORCE then light velocity must changes(acceleration produces) according to formula, "F=ma"(force acts on an object produces an acceleration in that object) while light has constant speed i.e. c=3x108m/s. How will you satisfy me about my both upper statements?