Question

During the journey of a spaceship from earth to moon and back, maximum fuel consumed:

• A. Against the gravitation of moon while reaching the moon
• B. Against the gravitation of earth in return journey
• C. Against the gravitation of earth in onward journey
• D. None of the above

Answer 1

The correct option is C

Against the gravitation of earth in onward journey

The explanation for the correct option:

In the case of option C,

1. Maximum fuel is consumed when the spaceship has to reach the greatest velocity.
2. We know that the velocity required to escape the gravitational pull of Earth is more than the velocity required to escape the gravitational pull of the Moon.
3. And the fuel consumed in the onward journey to the moon and return journey to Earth is less because there is no need to completely oppose the gravitational field, only cushioning the fall.
4. Thus, maximum fuel is consumed against the gravitation of earth on the onward journey.

The explanation for incorrect options:

In the case of option A,

1. While moving towards a planet, the force required to cushion the fall is directly proportional to the gravitational pull of the planet.
2. We know that the gravitational pull of Earth is greater than that of the Moon.
3. So the force needed to cushion the fall to Earth is greater than the force needed to cushion the fall to Moon.
4. To exert more force, more fuel is needed.
5. So the fuel needed to land on Moon is less than that for Earth.

In the case of option B,

1. We need more force to move away from a planet than towards it.
2. This is because, while returning the gravitational force of the planet is along the direction of motion and provides enough force to move the spaceship.
3. So fuel required in the return journey is less as no work needs to be done against the force of gravity.

In the case of option D,

1. We have already shown that option C, which claims that “Against the gravitation of earth in onward journey” is the maximum fuel consumed, is true.
2. So, it isn't possible that none of the options are correct

Hence, option C is correct.