1. The problem statement, all variables and given/known data An object that is moving at a constant speed velocity is acted upon by three forces. One force is 150 N along the x-axis, the second is 100 N along a direction making a counterclockwise angle of 120° with the x-axis. What is the magnitude of the third force? 2. Relevant equations Not sure, these are the only ones I THINK are remotely relevant (but I have no idea which is why I'm posting here) F_x = Fcosθ F_y = Fsinθ 3. The attempt at a solution I thought it would just be either 100 N (the same as the northwest force 120° from x-axis) or it would be something involving the Pythagorean Theorem (100^2 + f^2 = 150^2 or 100^2 + 150^2 = 150^2) Anyone? This is urgent. My whole class is confused.