Alice holds a flashlight motionless in her frame of reference. She shines it toward Bob, whom she measures to be approaching her at a speed of 0.9c, where c is the speed of light in vacuum. She measures the speed of the light leaving the flashlight to be c in her reference frame. Bob sees the light from Alice's flashlight and measures its speed. What speed does Bob measure for the light in his reference frame

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".