Question

If a rock is brought from the surface of the moon,
A) Its mass will change
B) Its weight will change not mass
C) Both mass and weight will change
D) Its mass and weight both will remain same

Answer 1

Hint: Recall that mass and weight of an object are not the same. Know what is meant by acceleration due to gravity and how it changes from earth to moon. Also we must know that the weight of an object is always affected by the value of acceleration due to gravity.

Complete step by step solution:
The amount of matter that a physical body contains is known as the mass of the body. It is the same everywhere in the universe and does not change with the location of the object. The mass of an object can never be zero as an object always contains matter and mass is a measure of matter. The mass is usually measured in units kilogram ($kg$) and grams ($g$). As there is no direction in the measure of mass, mass is a scalar quantity.

The force with which the earth attracts the object towards its centre is known as the weight of the body. The weight of the object depends on the acceleration due to gravity $g$ . The weight of the object increases or decreases with the increase or decrease in the value of $g$. Weight of an object can be zero if there is no gravity acting on it i.e. in space. As the weight of the object is always directed towards the centre of the earth, weight is a vector quantity.
Now that we know that the mass of an object is always constant and the weight of an object depending on the gravity, we can now answer the question.
The states a rock to be brought from the surface moon to earth. We know that the acceleration due to gravity on the moon and that on earth are not the same. This means, the weight of the object will not be the same on the surface on moon and earth and that will change accordingly with $g$ .
So the weight of the rock changes.
But we know that the mass of an object is always constant in the universe and does not change no matter where. This means that the mass of the rock does not change.
So we conclude that, if a rock is brought to earth from the surface of the moon then its mass will not change but its weight will change.

$\therefore $ Option $(B)$, the weight will change not mass, is the correct option.

Note: The acceleration due to gravity depends on the mass and radius of the object which pulls the smaller object towards its centre. The SI unit of $g$ is $m{s^{ - 2}}$ . Here, the value of $g$ depends on the mass and radius of earth and moon. This obviously states that the acceleration due to gravity on earth is greater than the acceleration due to gravity on the moon.
${g_{Earth}} > {g_{Moon}}$
${g_{Moon}} = \dfrac{{{g_{Earth}}}}{6}$
$ \Rightarrow weigh{t_{Earth}} > weigh{t_{Moon}}$
Weight of any object on earth is always $6$ times greater than the weight on the moon.