A 1000-kg airplane moves in straight flight at constant speed. The force of air friction is 1800 N. The net force on the plane is
zero
Zero. It's a conceptual question, because it gives more information than is necessary. The air friction force exceeds that of the plane's forward movement.
To find the net force on the plane, we need to consider the forces acting on it. In this case, we have two forces: the force of air friction (1800 N) and the force required to maintain constant speed.
Since the airplane is moving in straight flight at a constant speed, we know that the net force must be zero. This means that the force of air friction must be balanced by an equal and opposite force.
So, to find the net force on the plane, we need to subtract the force of air friction from the force required to maintain constant speed.
If we assume that there are no other external forces acting on the plane (such as thrust or gravitational forces), then the force required to maintain constant speed is also equal to 1800 N.
Therefore, the net force on the plane is:
Net Force = Force required to maintain constant speed - Force of air friction
= 1800 N - 1800 N
= 0 N
So, the net force on the plane is zero.