Question

An aeroplane flies at constant speed in a horizontal straight path. Two horizontal forces act on the plane. One is the thrust of the propellers that pushes it forward, and the other is the force of air resistance that acts in the opposite direction. Then:
A) Thrust force is more
B) Air resistance is more
C) Both thrust by propellers and air resistance are equal
D) Data insufficient

Answer 1

Hint: The aeroplane flies at a constant speed so in this condition we can use Newton's first law of motion and after that find the answer.

Complete step by step answer:
To find the answer first we should know about Newton's first law of motion.
Newton’s first law of motion:- First law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of external forces. This is also called the law of inertia.
As given in the question, that aeroplane flies at a constant speed and the net external force must be zero.
So when the aeroplane flies there are two types of forces that are working on it: first is thrust of the propeller that pushes it forward and the other force is air resistance that acts in the opposite direction and to fly the plane the net force must be zero.
So we can say that to produce the zero net force the thrust produced by the propeller and the air resistance are equal and are in the opposite direction.

Note: Thrust must be equal to or greater than drag for a plane to move forward with uniform speed or acceleration. The lift to the plane or the dynamics of the plane in the vertical plane is explained using Bernoulli’s Principle.