1. The problem statement, all variables and given/known data A missile is launched from a fighter jet cruising horizontally at a speed of 280 m/s, at an altitude of 1800 m. The initial velocity of the missile relative to the fighter jet is 160 m/s, in the forward direction. The missile is powered by its own engine, which provides it with a constant, horizontal acceleration of a = g/3. The vertical motion of the missile, however, is a free fall (as we neglect the effect of air friction). Take g = 9.80 m/s2. (a) How long does it take for the missile to reach the ground? (b) If the missile hits a tank on the ground, how far ahead of the plane horizontally was the tank when the missile was launched? Assuming that the tank has negligible speed compared with the missile. (c) What is the speed of the missile just before hitting the tank? (d) What angle does the velocity of the missile make with the ground just before it hits the tank? 2. Relevant equations Δx = Vixt x 1/2gt^2 Vf = Vi + at 3. The attempt at a solution I completed this whole problem then checked the answer key and it seems that my professor made gravity = 9.80 m/s^2 positive and i made gravity negative. I just wanted to know why and b/c i have a exam tonight and want to know when to make gravity positive in these types of questions.