Question

When we lower a bucket into the well to fetch water, the work done by the gravity is:
A. zero
B. unity
C. positive
D. negative

Answer 1

Hint: Gravitational force is an attractive force between two objects which tries to pull every two objects having mass together. The Universal Law of Gravitation was given by Sir Isaac Newton which states that; every object in the universe attracts every other object in the universe which is in existence.

Complete answer:
Gravitational force is the force of attraction that pulls two objects towards each other. This law was explained by Sir Isaac Newton with a low given by his. This law is popularly known as the law of gravitation.
Universal Law of gravitation:
“Every object in this universe attracts every other object by an attractive pull”.
This law explained more conceptually by the universal gravitation equation:
When two objects of mass ${{m}_{1}}$ and ${{m}_{2}}$(measured in kg) are separated by a distance $r$ the force of gravitation acting between the two bodies is given by:
$F=G\dfrac{{{m}_{1}}{{m}_{2}}}{{{r}^{2}}}$ …………………(1)
In equation (1), G is known as a gravitational constant which is applicable anywhere in the universe. The value of G is $6.67\times {{10}^{-11}}$.
From the above formula, we can say that the gravitational force is directly proportional to the mass in kg of the two objects and is inversely proportional to the square of the distance between the objects.
As the distance decreases, there will be an increase in the gravitational attraction between them and vice versa. This is known as the Inverse Square Law.
Consider 2 objects one as a bucket and the other is the earth itself. As the mass of the earth is way more than that of the bucket the gravitational pull will be more towards the earth. When a bucket is lower into a well to fetch water displacement is in the same direction as that of gravitational pull. Thus the work done by the gravitational force will be positive.

So, here we can conclude that the correct option which satisfies the conditions of the given question is option C.

Note: The gravitation law and gravitational equations are valid for every object in this universe. The object which has greater mass will attract the next object with a greater force of attraction. This is the main reason that everything on earth is attracted to the earth's surface. And we can walk on the ground due to this force of attraction only.