SUMMARY: The chapter on Gravitation in Class 9 Science explores the universal law of gravitation and its applications, including the motion of objects under the influence of gravity. KEY TOPICS: universal law of gravitation, gravitational force, acceleration due to gravity, free fall, mass and weight, thrust and pressure, Archimedes' principle, buoyancy, density, applications of gravitation
AEvery particle attracts every other particle with a force proportional to the product of their masses.
BOnly large objects attract each other with a gravitational force.
CGravitational force only acts on objects that are in motion.
DThe gravitational force is constant and does not depend on distance.
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Correct answer: Option 1 — Every particle attracts every other particle with a force proportional to the product of their masses.
Q21 Mark
Which of the following correctly defines gravitational force?
AThe force that pulls objects towards the center of the Earth.
BThe force that pushes objects away from the Earth.
CThe force that acts on objects in a vacuum only.
DThe force that depends on the shape of the objects involved.
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Correct answer: Option 1 — The force that pulls objects towards the center of the Earth.
Q31 Mark
What is the value of acceleration due to gravity (g) on the surface of the Earth?
A9.8 m/s²
B10 m/s²
C9.81 m/s²
D8.9 m/s²
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Correct answer: Option 3 — 9.81 m/s²
Q41 Mark
An object is in free fall. What can be said about its acceleration?
AIt is zero.
BIt is equal to the acceleration due to gravity.
CIt increases as the object falls.
DIt decreases as the object falls.
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Correct answer: Option 2 — It is equal to the acceleration due to gravity.
Q51 Mark
What is the difference between mass and weight?
AMass is a measure of the amount of matter, while weight is the force of gravity on that mass.
BMass changes with location, while weight does not.
CWeight is a scalar quantity, while mass is a vector quantity.
DMass is measured in Newtons, while weight is measured in kilograms.
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Correct answer: Option 1 — Mass is a measure of the amount of matter, while weight is the force of gravity on that mass.
Q61 Mark
Which of the following statements is true regarding thrust?
AThrust is the force applied perpendicular to the surface.
BThrust is always directed upwards.
CThrust does not affect pressure.
DThrust is independent of the area over which it is applied.
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Correct answer: Option 1 — Thrust is the force applied perpendicular to the surface.
Q71 Mark
According to Archimedes' principle, what happens to an object submerged in a fluid?
AIt experiences a buoyant force equal to its weight.
BIt sinks regardless of its density.
CIt experiences a buoyant force equal to the weight of the fluid displaced.
DIt floats only if it is less dense than the fluid.
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Correct answer: Option 3 — It experiences a buoyant force equal to the weight of the fluid displaced.
Q81 Mark
Which of the following factors does NOT affect the buoyancy of an object?
ADensity of the fluid.
BVolume of the object submerged.
CShape of the object.
DAcceleration due to gravity.
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Correct answer: Option 3 — Shape of the object.
Q91 Mark
What is the SI unit of density?
AKilogram per cubic meter (kg/m³)
BGram per cubic centimeter (g/cm³)
CNewton per cubic meter (N/m³)
DKilogram (kg)
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Correct answer: Option 1 — Kilogram per cubic meter (kg/m³)
Q101 Mark
If the mass of an object is doubled, what happens to its weight?
AIt remains the same.
BIt doubles.
CIt triples.
DIt halves.
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Correct answer: Option 2 — It doubles.
Q111 Mark
Which of the following is an application of gravitation?
AThe design of airplanes.
BThe motion of planets around the sun.
CThe functioning of a pendulum clock.
DThe operation of a car engine.
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Correct answer: Option 2 — The motion of planets around the sun.
Q121 Mark
What is the relationship between pressure, thrust, and area?
APressure is the product of thrust and area.
BPressure is equal to thrust divided by area.
CPressure is independent of thrust.
DPressure increases with area.
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Correct answer: Option 2 — Pressure is equal to thrust divided by area.
Q131 Mark
Which of the following best describes free fall?
AAn object falling under the influence of air resistance.
BAn object falling without any forces acting on it except gravity.
CAn object falling with a constant speed.
DAn object falling in a vacuum with no gravitational force.
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Correct answer: Option 2 — An object falling without any forces acting on it except gravity.
Q141 Mark
What happens to the weight of an object when it is taken to the Moon?
AIt increases.
BIt decreases due to lower gravity.
CIt remains the same as on Earth.
DIt becomes zero.
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Correct answer: Option 2 — It decreases due to lower gravity.
Q151 Mark
Which principle explains why ships float on water?
AArchimedes' principle
BNewton's third law
CBernoulli's principle
DPascal's law
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Correct answer: Option 1 — Archimedes' principle
Short Answer Questions10 questions
Q163 Marks
What is the universal law of gravitation?
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The universal law of gravitation states that every particle 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.
Q173 Marks
Define gravitational force and its significance in our daily lives.
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Gravitational force is the attractive force between two masses. It is significant as it keeps us grounded on Earth, governs the motion of celestial bodies, and influences various phenomena such as tides.
Q183 Marks
What is the value of acceleration due to gravity on Earth?
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The acceleration due to gravity on Earth is approximately 9.8 m/s². This value can vary slightly depending on altitude and geographical location.
Q193 Marks
Explain the concept of free fall.
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Free fall is the motion of an object under the influence of gravity alone, without any air resistance. During free fall, all objects accelerate at the same rate regardless of their mass.
Q203 Marks
Differentiate between mass and weight.
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Mass is the amount of matter in an object, measured in kilograms, and remains constant regardless of location. Weight is the force exerted by gravity on that mass, measured in newtons, and varies with the gravitational field strength.
Q213 Marks
What is thrust and how does it relate to pressure?
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Thrust is the force applied by an object in a specific direction, often used in the context of engines or rockets. Pressure is defined as force per unit area; thus, thrust can create pressure when applied over a surface area.
Q223 Marks
State Archimedes' principle and its application.
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Archimedes' principle states that a body immersed in a fluid experiences a buoyant force equal to the weight of the fluid displaced by it. This principle is applied in designing ships and submarines to ensure they float or submerge appropriately.
Q233 Marks
What is buoyancy and how does it affect objects in water?
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Buoyancy is the upward force exerted by a fluid on an object placed in it. It affects objects in water by determining whether they float or sink, depending on whether their weight is greater or less than the buoyant force.
Q243 Marks
How is density related to buoyancy?
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Density is the mass per unit volume of a substance. An object will float in a fluid if its density is less than that of the fluid, while it will sink if its density is greater, illustrating the principle of buoyancy.
Q253 Marks
Explain how gravitational force varies with distance.
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Gravitational force decreases with the square of the distance between two masses. As the distance increases, the gravitational attraction weakens significantly, following the inverse square law.
Long Answer Questions6 questions
Q266 Marks
Explain the universal law of gravitation and derive the formula for gravitational force between two masses. Provide an example to illustrate your explanation.
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The universal law of gravitation states that every point mass attracts every other point mass 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 formula is given by F = G(m1*m2)/r^2, where F is the gravitational force, G is the gravitational constant, m1 and m2 are the masses, and r is the distance between the centers of the two masses. For example, if we consider the Earth and an object on its surface, we can calculate the gravitational force acting on the object using its mass and the mass of the Earth, along with the radius of the Earth.
Q276 Marks
What is the difference between mass and weight? How does the acceleration due to gravity affect the weight of an object on different celestial bodies?
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Mass is a measure of the amount of matter in an object, and it remains constant regardless of location. Weight, on the other hand, is the force exerted by gravity on that mass and can vary depending on the gravitational field strength of the celestial body. The weight of an object is calculated using the formula W = mg, where W is weight, m is mass, and g is the acceleration due to gravity. For instance, an object will weigh less on the Moon than on Earth due to the Moon's lower gravitational acceleration, despite its mass remaining unchanged.
Q286 Marks
Describe free fall and the factors that affect it. How does free fall demonstrate the concept of gravitational acceleration?
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Free fall occurs when an object is falling under the influence of gravity alone, with no other forces acting on it, such as air resistance. In free fall, all objects experience the same acceleration due to gravity, which is approximately 9.81 m/s² on Earth. This means that regardless of their mass, all objects will fall at the same rate in a vacuum. This phenomenon demonstrates that gravitational acceleration is constant and independent of the object's mass, as shown by experiments like Galileo's famous dropping of balls from the Leaning Tower of Pisa.
Q296 Marks
Explain Archimedes' principle and its significance in understanding buoyancy. Provide an example of how this principle is applied in real life.
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Archimedes' principle states that any object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced by the object. This principle is significant in understanding why objects float or sink in fluids. For example, a ship floats because the weight of the water it displaces is equal to the weight of the ship. This principle is applied in designing ships and submarines, ensuring they displace enough water to remain buoyant while carrying their loads.
Q306 Marks
Discuss the concept of thrust and pressure in the context of gravitational forces. How do these concepts relate to the behavior of objects in fluids?
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Thrust is the force applied by an object to move through a fluid, while pressure is defined as the force exerted per unit area. In the context of gravitational forces, when an object is submerged in a fluid, the pressure increases with depth due to the weight of the fluid above it. This relationship explains why deeper objects experience greater buoyant forces. For example, a diver experiences increased pressure as they descend underwater, which affects their buoyancy and the forces acting on their body.
Q316 Marks
What is gravitational force, and how does it vary with distance? Explain with the help of a graph showing the relationship between gravitational force and distance.
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Gravitational force is the attractive force between two masses, which decreases as the distance between them increases. According to the universal law of gravitation, the force is inversely proportional to the square of the distance between the centers of the two masses. A graph of gravitational force versus distance would show a hyperbolic decline, indicating that as distance increases, the gravitational force rapidly decreases. This relationship is crucial in understanding how celestial bodies interact in space.
Assertion–Reason Questions8 questions
Q321 Mark
Assertion (A): The gravitational force between two objects increases as the distance between them decreases.
Reason (R): According to the universal law of gravitation, the force is inversely proportional to the square of the distance between the objects.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q331 Mark
Assertion (A): Weight is the same as mass.
Reason (R): Weight is a measure of the gravitational force acting on an object, while mass is a measure of the amount of matter in the object.
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Correct answer: Option 3 —
A is true, but R is false.
Q341 Mark
Assertion (A): An object in free fall experiences no gravitational force.
Reason (R): Free fall is the motion of an object under the influence of gravity alone.
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Correct answer: Option 4 —
A is false, but R is true.
Q351 Mark
Assertion (A): The acceleration due to gravity is constant at all points on Earth.
Reason (R): The acceleration due to gravity varies slightly depending on altitude and location on Earth.
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Correct answer: Option 4 —
A is false, but R is true.
Q361 Mark
Assertion (A): Archimedes' principle states that a body immersed in a fluid experiences a buoyant force equal to the weight of the fluid displaced.
Reason (R): This principle is a direct application of the laws of buoyancy and gravitation.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q371 Mark
Assertion (A): Thrust is defined as the force exerted per unit area.
Reason (R): Thrust is the total force acting on an object, while pressure is the force per unit area.
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Correct answer: Option 3 —
A is true, but R is false.
Q381 Mark
Assertion (A): The weight of an object is greater on the Moon than on Earth.
Reason (R): The gravitational pull on the Moon is weaker than that on Earth, resulting in lower weight.
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Correct answer: Option 4 —
A is false, but R is true.
Q391 Mark
Assertion (A): Density is defined as mass divided by volume.
Reason (R): This definition is crucial for understanding buoyancy and how objects behave in fluids.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Statement-Based Questions8 questions
Q401 Mark
Statement 1: The universal law of gravitation states that every point mass attracts every other point mass with a force that is directly proportional to the product of their masses.
Statement 2: Gravitational force is independent of the distance between the two masses.
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Correct answer: Option 2 —
Only Statement 1 is true.
Q411 Mark
Statement 1: The acceleration due to gravity on the surface of the Earth is approximately 9.8 m/s².
Statement 2: Weight is the measure of the gravitational force acting on an object.
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Correct answer: Option 1 —
Both statements are true.
Q421 Mark
Statement 1: Free fall occurs when the only force acting on an object is gravity.
Statement 2: In free fall, objects accelerate at a rate of 9.8 m/s² regardless of their mass.
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Correct answer: Option 1 —
Both statements are true.
Q431 Mark
Statement 1: Mass is a measure of the amount of matter in an object and is constant regardless of location.
Statement 2: Weight varies with the location of the object due to changes in gravitational pull.
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Correct answer: Option 1 —
Both statements are true.
Q441 Mark
Statement 1: Thrust is defined as the force acting perpendicular to the surface area.
Statement 2: Pressure is defined as the force acting parallel to the surface area.
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Correct answer: Option 4 —
Both statements are false.
Q451 Mark
Statement 1: Archimedes' principle states that a body submerged in a fluid experiences a buoyant force equal to the weight of the fluid displaced.
Statement 2: Density is defined as the mass of an object divided by its volume.
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Correct answer: Option 1 —
Both statements are true.
Q461 Mark
Statement 1: Buoyancy is the upward force exerted by a fluid on an object placed in it.
Statement 2: An object will float if its density is greater than the density of the fluid.
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Correct answer: Option 3 —
Only Statement 2 is true.
Q471 Mark
Statement 1: The gravitational force between two objects increases as the distance between them decreases.
Statement 2: The gravitational force is affected by the shape of the objects involved.
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Correct answer: Option 1 —
Both statements are true.
