An airplane performs a turn at constant speed and elevation so as to change its course by 180°. Let A and B designate the beginning and end points of the turn. Assuming that the change in mass of the plane due to fuel consumption is negligible, is the airplane’s momentum at A different from the airplane’s momentum at B? In addition, again neglecting the change in mass between A and B, is the total work done on the plane between A and B positive, negative, or equal to zero?