Question

Neil Armstrong brought back a rock from the moon. On earth

• A. The mass of the rock will change
• B. The weight of the rock will change
• C. Mass and weight will change
• D. None of the above

Hint:

Mass depends only on the matter in the rock, weight depends on the local pull of gravity.

Answer 1

The Correct Option is B

This question checks whether the difference between mass and weight is properly understood, which is a very old but often confused idea in basic physics.

1. The mass of the rock will change: Mass counts how much matter is packed into the rock, and that amount stays fixed no matter where the rock travels, whether on the moon, in a spacecraft, or on earth. So this option is incorrect.
2. The weight of the rock will change: Weight is a force, equal to mass times the gravitational pull at that location. The moon's gravity is roughly one sixth of earth's, so the very same rock felt a much smaller pull there. Once it lands on earth, the stronger gravity here acts on the same unchanged mass and produces a larger force, meaning heavier weight. This is why the weight changes while the mass stays put.
3. Mass and weight will change: This is incorrect because mass is not affected by gravity at all, only weight is.
4. None of the above: This is incorrect because one of the two quantities, weight, genuinely does change.

The rock's weight rises when it reaches earth simply because earth pulls on it harder than the moon did, even though the rock itself has not gained or lost any matter.

Let's summarize:

• Mass is constant everywhere; weight depends on local gravity.
• Earth's gravity is about six times that of the moon, so the same rock weighs more on earth.

The correct option is that the weight of the rock will change.