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- The law of gravitation asserts that the attraction between any two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance separating them. This principle is applicable throughout the universe and is known as a universal law.
- Gravitation is considered a relatively weak force unless it involves massive objects.
- The strength of gravity diminishes with increased altitude and also varies across Earth's surface, being weaker at the equator compared to the poles.
- An object's weight is defined as the gravitational force exerted on it by Earth, calculated as the product of its mass and the acceleration due to gravity.
- While weight can change depending on location, mass remains constant.
- Additionally, every object submerged in a fluid experiences a buoyant force.
- Objects with a density lower than the fluid will float, whereas those with a higher density will sink.
NCERT Based MCQ with Explanation:
1. Who formulated the Universal Law of Gravitation?
(a) Albert Einstein
(b) Isaac Newton
(c) Galileo Galilei
(d) Henry Cavendish
Explanation: Newton formulated the Universal Law of Gravitation, which states that every object in the universe attracts every other object with a force proportional to their masses and inversely proportional to the square of the distance between them.
2. What is the SI unit of gravitational constant (G)?
(a) N
(b) m/s²
(c) N·m²/kg²
(d) kg·m/s
Explanation: The gravitational constant (G) has units of Newton meter squared per kilogram squared (N·m²/kg²), as it relates to the force between masses and the square of the distance separating them.
3. The value of acceleration due to gravity (g) on Earth is approximately:
(a) 6.7 m/s²
(b) 8.8 m/s²
(c) 9.8 m/s²
(d) 11.2 m/s²
Explanation: The average acceleration due to gravity on Earth's surface is about 9.8 m/s². This value can vary slightly depending on altitude and geographical location.
4. What happens to the gravitational force between two objects if the distance between them is halved?
(a) It is quartered
(b) It is halved
(c) It doubles
(d) It quadruples
Explanation: According to the Universal Law of Gravitation, the force is inversely proportional to the square of the distance. If the distance is halved, the force increases by a factor of four.
5. The force that keeps the planets in orbit around the Sun is:
(a) Electromagnetic force
(b) Nuclear force
(c) Gravitational force
(d) Centrifugal force
Explanation: The gravitational force exerted by the Sun keeps the planets in their orbits.
6. The weight of an object on the Moon is approximately what fraction of its weight on Earth?
(a) 1/4
(b) 1/3
(c) 1/5
(d) 1/6
Explanation: The Moon's gravity is about 1/6th that of Earth, so objects weigh much less on the Moon.
7. Why do objects of different masses fall at the same rate in the absence of air resistance?
(a) Because mass doesn't affect acceleration
(b) Because gravitational force acts equally on all masses
(Ansc) Because the force of gravity is proportional to the mass, canceling out the mass effect
(d) Because air resistance slows heavier objects more
Explanation: The gravitational force on an object is proportional to its mass, but the acceleration due to gravity is the same for all objects, so they fall at the same rate in a vacuum.
8. Which of the following is true regarding mass and weight?
(a) Mass and weight are the same on Earth
(b) Mass changes depending on location
(c) Weight depends on gravitational force, but mass is constant
(d) Weight is constant, but mass changes in space
Explanation: Mass is an intrinsic property of matter and does not change with location, while weight depends on the gravitational force acting on the mass.
9. Which principle explains why ships float in water?
(a) Newton's third law
(b) Archimedes' principle
(c) Bernoulli's principle
(d) Pascal's law
Explanation: Archimedes' principle states that an object submerged in a fluid experiences an upward buoyant force equal to the weight of the displaced fluid, which allows ships to float.
10. What is the cause of tides on Earth?
(a) Earth's rotation
(b) Sun's heat
(c) Gravitational force of the Moon and the Sun
(d) Wind currents
Explanation: Tides on Earth are primarily caused by the gravitational pull of the Moon and, to a lesser extent, the Sun.
11. The force that pulls objects toward the center of the Earth is called:
(a) Frictional force
(b) Magnetic force
(c) Gravitational force
(d) Centripetal force
Explanation: Gravitational force is the attractive force that pulls objects toward the center of the Earth.
12. The SI unit of weight is:
(a) Kilogram
(b) Newton
(c) Joule
(d) Meter
Explanation: Weight is a force, and the SI unit of force is the Newton (N).
13. What is the formula to calculate weight (W) of an object?
(a) W = m × v
(b) W = m × g
(c) W = F × d
(d) W = m / g
Explanation: The weight of an object is the force exerted by gravity on it, and it is calculated as mass (m) times the acceleration due to gravity (g).
14. The value of gravitational acceleration (g) on the Moon is approximately:
(a) 9.8 m/s²
(b) 4.9 m/s²
(c) 1.6 m/s²
(d) 2.4 m/s²
Explanation: The gravitational acceleration on the Moon is much weaker than on Earth, with a value of about 1.6 m/s².
15. When the distance between two masses is tripled, the gravitational force between them becomes:
(a) 9 times smaller
(b) 9 times larger
(c) 3 times smaller
(d) 3 times larger
Explanation: The gravitational force is inversely proportional to the square of the distance between the masses. If the distance is tripled, the force becomes 1/9 of the original.
16. Which of the following best describes mass?
(a) The amount of matter in an object
(b) The force of gravity acting on an object
(c) The space an object occupies
(d) The weight of an object
Explanation: Mass is the measure of the amount of matter in an object and remains constant regardless of location.
17. What is the cause of Earth's gravitational force?
(a) Its magnetic field
(b) Its rotation
(c) Its mass
(d) Its atmosphere
Explanation: The gravitational force of Earth is due to its mass, which causes it to attract other objects toward its center.
18. In which of the following conditions does an object experience free fall?
(a) When falling in water
(b) When falling under the influence of air resistance
(c) When only gravitational force acts on it
(d) When the object is in space
Explanation: Free fall occurs when an object is falling solely under the influence of gravity, with no other forces like air resistance acting on it.
19. Which quantity remains constant in free fall?
(a) Velocity
(b) Mass
(c) Weight
(d) Acceleration
Explanation: In free fall, the acceleration due to gravity (g) remains constant at 9.8 m/s² near Earth's surface.
20. Why does a feather fall more slowly than a stone through the air?
(a) Due to less gravitational force on the feather
(b) Because of air resistance
(c) Because the feather has less mass
(d) Because the feather has more mass
Explanation: The feather falls more slowly due to air resistance acting on it, not because of its mass or gravitational force.
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