Gravitation
Multiple Choice Questions
1. Two objects of different masses falling freely near the surface of moon would
(a) have same velocities at any instant
(b) have different accelerations
(c) experience forces of same magnitude
(d) undergo a change in their inertia
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Answer
Answer is (a) have same velocities at any instant
Explanation:
Acceleration of an object depends on acceleration due to gravity irrespective of its mass. Hence object under free fall have the same velocities.
(a) is same on equator and poles
(b) is least on poles
(c) is least on equator
(d) increases from pole to equator
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Answer
Answer is (c) is least on equator
Explanation:
The value of acceleration due to gravity is least on equator because distance between surface of the earth and its centre is more on equator than in poles.
(a)
(b)
(c)
(d)
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Answer
Answer is (a) F/4
(b) will move along a straight line towards the centre of the circular path
(c) will move along a straight line tangential to the circular path
(d) will move along a straight line perpendicular to the circular path away from the boy
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Answer
Answer is (c) will move along a straight line tangential to the circular path
Explanation:
At any instance of time object in circular motion tend to be in rectilinear motion. Object keeps on moving due to centripetal force and it moves along a straight line tangential to the circular path when strings breaks.
(a)
(b)
(c)
(d)
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Answer is (d)
(a) depends on the value of
(b) is used only when the earth is one of the two masses
(c) is greatest at the surface of the earth
(d) is universal constant of nature
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Answer
Answer is (d) is universal constant of nature
Explanation:
(a) the earth and a point mass only
(b) the earth and Sun only
(c) any two bodies having some mass
(d) two charged bodies only
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Answer
Answer is (c) any two bodies having some mass
(a) depends on mass of earth only
(b) depends on radius of earth only
(c) depends on both mass and radius of earth
(d) is independent of mass and radius of the earth
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Answer
Answer is (d) is independent of mass and radius of the earth
Explanation:
(a) 14 times
(b) 4 times
(c) 12 times
(d) unchanged
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Answer
Answer is (b) 4 times
Explanation:
(a) gravity
(b) wind
(c) clouds
(d) earth’s magnetic field
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Answer
Answer is (a) gravity
(a) gravitational potential
(b) acceleration due to gravity
(c) gravitational field
(d) universal gravitational constant
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Answer
Answer is (d) universal gravitational constant
Explanation:
Here point masses are separated by unit distance
Hence
Hence
(a) zero
(b) infinite
(c)
(d) 1/R2 times the weight at surface of the earth
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Answer
Answer is (a) zero
Explanation:
At the centre of the earth acceleration due to gravity is zero. Since weight is the product of mass and gravity. Weight of object at the centre of the earth will be zero.
(a)
(b)
(c)
(d)
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Answer
Answer is (a)
Explanation:
Object of weight displace
(a) maximum when length and breadth form the base
(b) maximum when breadth and width form the base
(c) maximum when width and length form the base
(d) the same in all the above three cases
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Answer
Answer is (b) maximum when breadth and width form the base
Explanation:
Surface area and pressure are inversely proportional. Pressure will be maximum when surface area is minimum hence the answer is maximum when breadth and width form the base.
(a)
(b) F2 is very much greater than
(c) F1 is only a little greater than F2
(d) F1 and F2 are equal
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Answer
Answer is (d) F1 and F2 are equal
Explanation:
Netwon’s third law of motion states that for every action there is equal and opposite reaction. Hence F1 and F2 are equal.
Short Answer Questions
16. What is the source of centripetal force that a planet requires to revolve around the Sun? On what factors does that force depend?
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Answer
Gravitational force is the source of centripetal force required to revolve around the sun. This force depends on distance between the planet and sun along with their masses.
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Answer
Both the stones reach the ground simultaneously as they are dropped from same height and their intial velocity will be same .
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If there is no gravitational pull from the earth moon start to move in a straight line tangent to its circular path.
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Value of
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Weight of person is
This proves acceleration due to gravity on moon is
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Density of earth
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Sun provides enough centripetal force to keep earth in its orbit and the earth provides centrifugal force due to its motion. These two force balance each other which prevents earth from falling into sun.
Long Answer Questions
23. How does the weight of an object vary with respect to mass and radius of the earth. In a hypothetical case, if the diameter of the earth becomes half of its present value and its mass becomes four times of its present value, then how would the weight of any object on the surface of the earth be affected?
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Answer
Let
Then
Weight of the object
Original weight
Hypothetically
Then, weight
Weight will be 16 times.
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Answer
Force of attraction between two masses separated by distance
Gravitational force is directly proportional to the product of the masses of two bodies and inversely proportional to the square of the distance between them.
Bodies thrown from same height fall with same speed irrespective of their mass. This is due to acceleration due to gravity.
This equation shows that acceleration due to gravity depends on mass of the earth and radius of the earth. Henec tow brick tied will not fall faster than single one.
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Answer
as
As the acceleration remain same ratio between two objects remain same. In this case acceleration does not depend upon mass and size.
(b) A ball weighing
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Answer
i) Buoyant force,
Volume and density of an object decides its Buoyancy. Cube will experience a greater byoyancy in saturated solution. If cube is reduces to
(ii) The magnitude of the buoyant force given by
where
Hence Volume of solid