Gravity Questions

What is Gravity?

Every entity or object in this universe employs a gravitational force or pulls on every other object. Depending on the masses of the objects, the strength of this pull is defined. The force that keeps the moon around the earth and the planets in their respective orbit around the sun is gravity.

So, gravity is a force that attracts an object towards the centre of the earth or any other physical body having mass. In 1687, gravity was first discovered by Sir Isaac Newton. He noticed an apple falling while sitting under an apple tree. This made him determine why the apple is falling instead of going up or left or right. And thus, it was observed to him that an unknown force was at play; Newton called it gravity and his theory is titled Newton’s law of Universal Gravitation.

Measuring Gravity

The force of gravity, defined by Sir Isaac Newton, says:

“In the universe, every particle of matter attracts every other particle with a force that is inversely proportional to the square of the distance between them directly proportional to the product of the masses of their masses particles.”

Mathematically, it can be written as:

Where,

• F = Force
• Masses of the interacting objects are m₁ and m₂
• Distance between the centre of the masses is r
• G = gravitational constant (6.674×10⁻¹¹ m³⋅kg⁻¹⋅s⁻²)

Hence, the above equation gives the magnitude of the force, which is an attractive force that is always directed towards the other object. We can also conclude that objects with heavier mass have more gravity and anything that has mass has gravity. The intensity of the gravitational pull between two objects depends on their distance.

Important Questions on Gravity

1) The mass of an object can never be zero, but the weight of an object can be zero.

a) True

b) False

Correct Option: (a)

Explanation: When the net gravitational force acting on the object is zero, the weight of an object will become zero. But, since mass is a property of matter, the mass of an object can never be zero.

2) At the equator, what happens to the value of g if the earth stops rotating?

a) First increases and then decreases

b) Decreases

c) No effect

d) Increases

Correct Option: (d)

Explanation: At the equator, g_e=g-Rω²

When ω=0, g_e=g

If the earth stops rotating, the value of g increases.

3) Why do the astronauts experience weightlessness in the international space station?

a) Acceleration due to gravity is zero at that height

b) Because they are falling towards the earth

c) Their spacesuits are specially designed for this purpose

d) At that height, the gravity of the moon and earth cancel out each other

Correct Option: (b)

Explanation: The weightlessness experienced by the astronauts in the ISS is the consequence of this freefall. Since the parabolic trajectory of the free fall of the ISS is at such high velocity that it orbits the planet.

4) In the case of the centre of gravity, which of the following statements is true?

a) Centre of gravity only lies outside the body

b) Centre of gravity lies inside the body

c) Irrespective of the shape, the centre of gravity lies at the centre of the body

d) Centre of gravity may lie inside or outside the body

Correct Option: (d)

Explanation: Centre of gravity does not necessarily lie inside the body because it is a point in the body where the resultant force acts; it may lie inside or outside the body.

5. A satellite doesn’t need any fuel to rotate around the earth.

a) True

b) False

Correct Option: (a)

Explanation: The gravitational force between the earth and the satellite provides the centripetal force, due to which the satellite moves in a circular orbit.

6) What velocity is needed to project an elephant and an ant out of the earth into space?

a) Higher velocity is needed to project the elephant out of the earth

b) Ant should be projected with a lesser velocity

c) Elephant cannot be projected to space

d) Both should be projected with the same velocity

Correct Option: (d)

Explanation: Since the escape velocity is given by v_e=√2gR, and it does not depend upon the mass of the projected body, the same velocity is needed to project an elephant and an ant into space.

7) While revolving in a circular orbit, an astronaut throws a spoon outside. What will happen to the spoon?

a) Spoon will reach the earth’s surface

b) Spoon will escape out of the universe

c) Spoon will remain stationary

d) Spoon will continue to move in a circular orbit

Correct Option: (d)

Explanation: If a spoon is thrown outside while revolving in a circular orbit, the spoon will continue to rotate in the same circular orbit.

8) Which among the following laws is valid in all natural processes?

a) Faraday’s law

b) Newton’s law of gravitation

c) Snell’s law

d) Lenz’s law

Correct Option: (b)

Explanation: Newton’s law of gravitation states that, with force directly proportional to the product of their masses and inversely proportional to the square of the distance between them, every object in the universe attracts every other object. Hence Newton’s law is valid for all natural processes.

9) Which among the following is the correct value of the universal gravitational constant?

a) 9.81 m/s²

b) 1.602 x 10^-19 C

c) 6.67 x 10^-11 N m²/kg²

d) 6.022 x 10²³

Correct Option: (b)

Explanation: Here, Avogadro number is 6.022 x 10²³

Universal gravitational constant is equal to 6.67 x 10^-11 N m²/kg²

1.602 x 10^-19 C = Charge of a proton

The acceleration due to gravity is 9.81 m/s²

10) The escape velocity of an object does not depend on its mass.

a) True

b) False

Correct Option: (a)

Explanation: The escape velocity of an object does not depend on its mass; rather, it only relies on the mass of the planet through which it is escaping.

The relation is as given below;

Escape velocity (v) = [(2*G*M)/R]^1/2

Radius of planet = R

Mass of planet = M

Practice Questions

1) What is Newton’s universal law of gravitational attraction?

2) What is gravity?

3) What is escape velocity?

4) What is the escape velocity of earth?

5) What is the relationship between gravity and weight?

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