Free Gravitation MCQs with Answers

101. The gravitational force is responsible for the motion of_:

• A. Atom round the nucleus
• B. Motor car on the road
• C. A body round the axes
• D. Planet around the sun

Explanation: The gravitational force Fg is responsible for the motion of planets around the Sun. According to Newton's law of universal gravitation, every mass in the universe attracts every other mass with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. In the case of planets orbiting the Sun, this gravitational force provides the centripetal force needed to keep the planets in their orbits, following Kepler's laws of planetary motion.

102. The mass of Earth can be determined by using:

• A. Kepler's law
• B. The Cavendish experiment
• C. Newton's second law of motion
• D. Universal law of gravitation

Explanation: The universal law of gravitation, proposed by Sir Isaac Newton, states that every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Mathematically, it is expressed as F=Gm1m2/r2 , where F is the gravitational force, G is the gravitational constant, m1 and m2 are the masses of the interacting objects, and r is the distance between their centers. Using this law, along with other known constants and measurements, the mass of the Earth can be calculated. In conclusion, the primary method for determining the mass of the Earth is through experiments like the Cavendish experiment, which utilizes the principles of Newton's universal law of gravitation.

103. Free falling bodies develop a state of:

• A. Weight lessening
• B. Dynamic equilibrium
• C. Static equilibrium
• D. Rest

Explanation: B is the correct answer. Dynamic equilibrium occurs when an object is in motion with a constant velocity. In the case of free fall, once the object has overcome air resistance and other factors, it falls with a constant acceleration due to gravity. This constant velocity is considered dynamic equilibrium in the context of free fall.

104. The law of gravitation was introduced by:

• A. Pascal
• B. Boyle
• C. Huygen
• D. Newton

Explanation: Sir Isaac Newton, an English mathematician and physicist, introduced the law of universal gravitation in his work "Philosophiæ Naturalis Principia Mathematica" ("Mathematical Principles of Natural Philosophy") published in 1687. The law states that every mass attracts every other mass in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. The law of gravitation is one of Newton's most significant contributions to physics.

105. If the speed of rotation of the Earth is increased, the mass lying on its surface will be:

• A. Increased in weight
• B. Decreased in weight
• C. Some time increase & some time decrease
• D. Have no change in weight

Explanation: D is the correct option. The weight of an object is determined by the gravitational force acting on it, which depends on the mass of the object and the mass of the Earth. The Earth's rotation speed, within reasonable limits, does not significantly impact the weight of objects on its surface.

106. Weightlessness experienced while orbiting the earth in space ship is the result of:

• A. Inertia
• B. Acceleration
• C. Zero gravity
• D. Centre of gravity

Explanation: Weightlessness is often colloquially referred to as "zero gravity,". The correct term is microgravity. In orbit, there is still a gravitational force acting on the spaceship and its contents; it's just that everything is in a state of continuous free fall, creating the sensation of weightlessness.

107. A spoon is gently detached from a geostationary satellite. The spoon will:

• A. Now follow an irregular path
• B. Fall to the Earth
• C. Continue to move with satellite
• D. Follow a parabolic path

Explanation: Option C means that when the spoon is released from the satellite, it will continue to travel at the same velocity it had before, along the orbital path, due to inertia.

108. A man standing in an elevator is acted upon by:

• A. Four forces
• B. Three forces
• C. Two forces
• D. One force

Explanation: In some situations, we may simplify the analysis to consider only two forces: gravity and the normal force. If the elevator is not accelerating vertically, the net force is zero, and the normal force equals the force of gravity, resulting in no vertical motion.

109. A rocket can go vertically upward in Earth's atmosphere because:

• A. It is lighter than air
• B. Of gravitational pull of Earth
• C. It has a fan, which displaces more air per unit time then, the weight of rocket
• D. Of the force exerted on the rocket by gases ejected by it

Explanation: D is the correct answer. Rockets work on the principle of action and reaction (Newton's third law of motion). As the rocket expels gases at high speed through its rocket nozzles, the expelled gases exert a force (thrust) on the rocket in the opposite direction. This thrust is greater than the weight of the rocket, allowing it to lift off and move upward.

110. The time period of a satellite in a circular orbit round a planet is independent of:

• A. Mass of the satellite
• B. The radius of the planet
• C. The mass planet
• D. All of these

Explanation: The time period of a satellite does not depend on the mass of the satellite. According to Kepler's Third Law of Planetary Motion, the square of the orbital period (time period) of a satellite is directly proportional to the cube of the semi-major axis of its orbit. The mass of the satellite is not a factor in this relationship.