Question

What force causes (a) an automobile, (b)a propeller driven airplane, and (c) a rowboat to move?

Answer 1

Hint: In order to solve this question we need to understand that motion of the body. So according to Newton’s first law which states that every object wants to be in rest or in motion unless some external unbalanced force acts on it. So whenever an object moves, the force required to move it must be greater than the opposing force. Here, we will discuss the type of force acting on each of the asked systems.

Complete answer:
(a) Consider an automobile at rest, suppose some external force acts on it (generated due to burning of fuel) acts on it then it needs to overcome the static friction between tyres of the automobile and the road. So when friction becomes equal to applied force there would be no net acceleration in the body and then the body moves with constant velocity.Hence, Frictional force causes an automobile to move.

(b) Consider an airplane travelling in air, then due to air resistance, air tries to push it backward in order to oppose its motion, so a propeller engine of an airplane throws the air backwards so that airplane could move forward in air. Hence, the force due to atmospheric air pressure causes propeller driven airplanes to move.

(c) In order to move a row boat in water, the person sitting on rowboat must push the water backward so that it can move forward by the reaction of water. Hence, the force due to water pressure causes a rowboat to move.

Note: It should be remembered that Newton’s third law states that for every action there is an equal and opposite reaction, so when a person sitting on a rowboat pushes back the water then water pushes the rowboat in forward direction, so in this way it moves on water. Also terminal velocity is that velocity of an object which is constant in nature and the object is only when the net force on the body is zero.