Question

During the journey of spaceship from earth to moon and back, the maximum fuel consumed is:
A) Against the gravitation of earth in return journey.
B) Against the gravitation of earth in onward journey.
C) Against the gravitation of the moon while reaching the moon.
D) None of the above.

Answer 1

Hint: As per Newton's law every object in this universe attracts every other object with an attractive force, where distance between the two objects is inversely proportional to the square of the distance.
Using the concept of above law we will analyze the motion of spacecraft away from the earth and back to the earth.

Complete solution:
Let's discuss Newton's law in detail first and then we will conclude the gravitational force against earth or in the direction of gravitational force.
Newton's law of universal gravitation is usually stated as that every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
In the similar manner, when we go out from the earth's surface towards the surface of moon, force of gravitation acts as a resistance in not allowing the spaceship to move away from the surface of earth and thus spaceship has to put in an extra effort to move out of the surface of the earth because the gravitational pull exerted by earth is more than that of moon, hence fuel consumption will be more.
On the other hand, when the spaceship goes back to the earth's surface from the surface of moon gravitational force will act in pulling the spaceship towards it, and thus the consumption of fuel will be less.

Thus, option (B) is correct.

Note: Gravitational force keeps us attached to the earth, holds the air down, gravity makes the surface roughly spherical, gravity keeps all the celestial objects revolving in the orbit, gravity brings the rain down even after the evaporation of water from the earth's surface.