1. The problem statement, all variables and given/known data I am sort of reviving this thread. https://www.physicsforums.com/showthread.php?t=182511 My question is the same. I understand and agree with what fisix responded a few years ago. 2. Relevant equations cos( θ)= v_cart / v_bullet 3. The attempt at a solution I can gather that in the reference frame of the cart, the bullet will appear to just go straight up and straight down. And, in the reference frame of the ground, the bullet will look following a parabolic path. Nevertheless, I cannot discern how to obtain the angle. It seems to me that it has to be lesser or equal than pi/2. I am not looking for the direct answer, but I just don't know how to proceed. Thank you.