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Gravitation is the force of attraction occurring between any two bodies attracting the body towards the center. Gravitation, or gravity, is the force that attracts two bodies together. The gravitational force is a central force that works along the line connecting the centers of the two masses and is solely dependent on the distance between the test mass and the source mass. According to Newton’s law of gravitation, “Every particle in the universe attracts every other particle with a force whose magnitude is directly proportional to the product of their masses and inversely proportional to the square of the distance between their center.
An example of gravitation is the fruits falling from a tree downwards due to gravitational pull.
Multiple Choice Questions
Ques.1 Force is a physical quantity that depends on
- Mass
- Speed
- Acceleration
- Both a and c
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Ans. d. Both a and c
Explanation: According to the second law of motion when a force is applied to an object, the object moves in the same direction as the force. It produces acceleration i.e rate of change of velocity in the object. Thus, the force is the product of mass and acceleration.
Ques.2 The first law of motion introduced the concept of
- Action and reaction
- Inertia
- Kinetic energy
- Momentum
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Ans. b. Inertia
Explanation: The first law of motion states that every object remains at uniform motion unless compelled to change its state by an external force. This means that the object can not start, stop or change its direction by itself. The first law of Newton is otherwise known as the law of inertia.
Ques.3 What is the term for the force that binds the atmosphere round the earth
- Force of gravity
- Nuclear force
- Atmospheric pressure
- None
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Ans. a. Force of gravity
Explanation: The planet attracts all the objects towards its center. This is called the force of gravity. It is a strong force that unites the atmosphere around the earth. At the earth's surface about 9.8 meters per second is the acceleration of gravity. Gravity is the most dominant force though it the weakest of the four fundamental forces of nature.
Ques.4 What will be the required force to produce an acceleration of 9.8m/s² on the body of weight 9.8 N?
Take g = 9.8 m/s2
- 1 N
- 4.9 N
- 19.6 N
- 9.8 N
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Ans. d. 9.8N
Explanation: Force = mass × acceleration
Given acceleration (a) = 9.8 m/s2
Bodyweight = 9.8 N
Since weight of the body = mg
⇒ Mass = weight/g = 9.8/9.8= 1 kg
We know,
F = m × a
F = 1 kg × 9.8 m/s2
F = 9.8 N
Therefore, 9.8 N is the required amount of force.
Ques.5 Magnitude of force in action and reaction is
- Depending on the time of reaction
- Always equal
- Always unequal
- It may be equal or unequal
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Ans. b. always equal
Explanation: The third law of Newton states that when a body exerts a force on another body, the first one experiences a force that is equal in magnitude in the opposite direction of the exerted force. This simply means that the magnitude of the forces is equal. The force direction on the first object is opposite to the force direction on the second object.
Example –
- When the swimmer swims he pushes his body against the pool wall with his feet and then in return he swims or accelerates in the direction opposite to that of his push.
- Even the rock climber while pulling the rope downwards to push themselves upward is also an example of the third law of motion.
Ques.6 What will be the mass of a boy who weighs 450N?
- 45.9 kg
- 450 kg
- 459 kg
- 4.5 kg
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Ans. a. 45.9 kg
Explanation: Weight (W) = mass(M) × acceleration due to gravity (g = 9.8m/s2)
Weight of the girl given = 450 N
W = m g = m × 9.8 = 450
Mass of the boy (m) = 450/9.8 = 45.9 kg.
Ques.7 If the relative density of a substance is 0.8 then calculate the density of the substance.
- 1200 kg/m3
- 1100 kg/m3
- 900 kg/m3
- 800 kg/m3
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Ans. d. 800 kg/m3
Explanation: The density of water is 1000 kg / m3
Relative density = density of the substance/density of water
The density of the substance = relative density × density of water
Density of substance = 0.8 × 1000
Density of water = 800 kg/m3
Ques.8 The atmosphere containing a large number of gases is held to the Earth due to
- Winds
- Clouds
- Gravity
- Earth's magnetic field
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Ans. c. gravity
Explanation: Gravity or gravitation is the universal force of attraction working between all matters. The atmosphere of the Earth is covered with the layer of gases commonly known as air, retained by the gravitational force of the earth. The air surrounds the planet earth and it forms the planetary atmosphere. The atmosphere of the earth protects life on the earth by generating pressure, allowing for liquid water to exist on the surface of the earth, absorbing ultraviolet radiation, warming the surface, controlling the heat, and decreasing the extreme temperatures between day and night.
9.807 m/s2 is the gravitational force of the Earth.
Ques.9 Newton's law of gravitation is grounded in
- Archimedes principle
- Kepler's first law
- Kepler's third law
- Kepler's second law
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Ans. d. Kepler's second law
Explanation: The law of universal gravitation states that the force of gravity affects mass in the universe. Also, the strength of the gravity between the two objects depends on the masses of the objects and the distance between them.Out of these general rules, Newton made it possible to showcase that all of Kepler's descriptive laws for orbits followed as a straight consequence. When Kepler's second law and Newton's law are combined, they imply that the force holding the planet in its orbit is constantly changing the planet's velocity, so that it follows a direction towards the sun from the planet, a proportional product of the sun and planet masses, and inversely proportional to the square of the planet-sun preparation.
The planets obey the same law of motion as objects on the surface of the earth. Newton's law of gravitation is thus grounded in Kepler's second law.
Ques.10 The mass of the object is 88 kg then what will be its weight on the moon?
- 148.34
- 143.44
- 862.44
- 132.33
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Ans. b. 143.44
Explanation: Mass given = 88kg
Acceleration on the moon due to gravity = 1.63m/s2
As per the second law of motion,
Weight (W) = mg
Weight = 88 × 1.63
Weight = 143.44
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