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State the universal law of gravitation.
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Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth.
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What do you mean by free fall?
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What do you mean by acceleration due to gravity?
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What are the differences between the mass of an object and its weight?
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Why is the weight of an object on the moon 1/6th its weight on the earth?
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Why is it difficult to hold a school bag having a strap made of a thin and strong string ?
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What do you mean by buoyancy ?
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How does the force of gravitation between two objects change when the distance between them is reduced to half?
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Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?
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What is the magnitude of the gravitational force between the earth and a 1 kg object on its surface? (Mass of the earth is 6 x 1024 kg and radius of the earth is 6.4 x 106 m)
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The earth and the moon are attracted to each other by gravitational force. Does the earth attract the moon with a force that is greater or smaller or the same as the force with which the moon attracts the earth? Why?
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If the moon attracts the earth, why does the earth not move towards the moon?
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What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?
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What is the importance of universal law of gravitation?
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What is the acceleration of free fall?
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What do we call the gravitational force between the earth and an object?
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Amit buys few grams of gold at the poles as per the instruction of one of his friends. He hands over the same when he meets him at the equator. Will the friend agree with the weight of gold bought? If not, why? [Hint: The value of g is greater at the poles than at the equator.]
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Why will a sheet of paper fall slower than one that is crumpled into a ball?
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Gravitational force on the surface of the moon is only 1/6 as strong as gravitational force on the earth. What is the weight in Newton’s of a 10 kg object on the moon and on the earth?
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A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate
(i) the maximum height to which it rises,
(ii) the total time it takes to return to the surface of the earth.
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A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the ground.
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A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s2, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?
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Calculate the force of gravitation between the earth and the sun, given that the mass of the earthkg and of the sun The average distance between the two is
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A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s-1. Calculate when and where the two stones will meet.
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A ball thrown up vertically returns to the thrower after 6 s. Find
(a) the velocity with which it was thrown up,
(b) the maximum height it reaches, and
(c) its position after 4 s.
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Why does an object float or sink when placed on the surface of water?
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You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
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You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?
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In what direction does the buoyant force on an object immersed in a liquid act?
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Why does a block of plastic released under water come up to the surface of water?
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The volume of 50 g of a substance is 20 cm3. If the density of water is 1 g cm-3 will the substance float or sink?
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The volume of 500 g sealed packet is 350 cm3. Will the packet float or sink in water if the density of water is 1 g cm-3 ? What will be the mass of the water displaced by this packet?
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question_answer34)
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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question_answer35)
The value of acceleration due to gravity
(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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question_answer36)
The gravitational force between two objects is F. If
masses of both objects are halved without changing distance between them, then
the gravitational force would become
(a) F/4 (b) F/2
(c) F (d) 2F
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question_answer37)
A boy is whirling a stone tied with a string in an
horizontal circular path.
If the string breaks, the stone
(a) will continue to move in the circular path
(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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question_answer38)
An object is put one by one in three liquids having
different densities. The object floats with and parts of their
volumes outside the liquid surface in liquids of densities and , respectively. Which
of the following statement is correct?
(a) (b) (c) (d)
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question_answer39)
In the relation ,
the quantity G
(a) depends on the value of g at the place of observation
(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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question_answer40)
Law of gravitation gives the gravitational force between
(a) the earth and a point mass only (b)
the earth and the sun only
(c) any two bodies having some mass (d)
two charged bodies only
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question_answer41)
The value of quantity G in the law of gravitation
(a) depends on mass of the earth only
(b) depends on radius of earth only
(c) depends on both mass and radius of the earth
(d) is independent of mass and radius of the earth
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question_answer42)
Two particles are placed at some distance. If the mass of
each of the two particle is doubled, keeping the distance between them
unchanged, the value of gravitational force between them will be
(a)times
(b) 4 times (c) times
(d) unchanged
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question_answer43)
The atmosphere is held to the earth by
(a) gravity (b) wind (c)
clouds (d) earth's magnetic field
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question_answer44)
The force of attraction between two unit point masses
separated by a unit distance is called
(a) gravitational potential (b)
acceleration due to gravity
(c) gravitational field (d)
universal gravitational constant
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question_answer45)
The weight of an object at the centre of the earth of
radius R, is
(a) zero (b) infinite
(c) R times the weight at the surface of the earth
(d) times
the weight at the surface of the earth
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question_answer46)
An object weighs 10 N in air. When immersed fully in
water, it weighs only 8 N. The weight of the liquid displaced by the object
will be
(a) 2N (b) 8N (c)
10N (d) 12N
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question_answer47)
A girl stands on a box having 60 cm length, 40 cm breadth
and 20 cm width in three ways. In which of the following cases, pressure
exerted by the brick will be
(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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question_answer48)
An apple falls from a tree because of gravitational
attraction between the earth and apple. If is the magnitude of
force exerted by the earth on the apple and is the magnitude of force
exerted by apple on earth, then
(a) is
very much greater than (b)
is very much greater
than
(c) is
only a little greater than (d)
and are equal
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question_answer49)
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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question_answer50)
On the earth, a stone is thrown from a height in a direction parallel to the
earth's surface while another stone is simultaneously dropped from the same
height. Which stone would reach the ground first and why?
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question_answer51)
Suppose gravity of the earth suddenly becomes zero, then in which direction
will the moon begin to move if no other celestial body affects it?
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question_answer52)
Identical packets are dropped from two aero planes, one above the equator
and the other above the North Pole, both at height h. Assuming all conditions
are identical, will those packets take same time to reach the surface of earth.
Justify your answer.
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question_answer53)
The weight of any person on the moon is about 1/6 times that on the earth.
He can lift a mass of 15 kg on the earth. What will be the maximum mass, which
can be lifted by the same force applied by the person on the moon?
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question_answer54)
Calculate the average density of the earth in terms of g, G and R.
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question_answer55)
The earth is acted upon by gravitation of the sun, even though it does not
fall into the sun. Why?
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question_answer56)
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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question_answer57)
How does the force of attraction between the two bodies depend upon their
masses and distance between them? A student thought that two bricks tied
together would fall faster than a single one under the action of gravity. Do
you agree with his hypothesis or not? Comment.
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question_answer58)
Two objects of masses and
having the same size
are dropped simultaneously from heights and respectively. Find
out the ratio of time they would take in reaching the ground. Will this ratio
remain the same if (i) one of the objects is hollow and the other one is solid
and (ii) both of them are hollow, size remaining the same in each case. Give reason.
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question_answer59)
(i) A cube of side 5 cm is immersed in water and then in
saturated salt solution. In which case will it experience a greater buoyant force.
If each side of the cube is reduced to 4 cm and then immersed in water, what
will be the effect on the buoyant force experienced by the cube as compared to
the first case for water. Give reason for each case.
(ii) A ball weighing 4 kg of density 4000 is completely
immersed in water of density .
Find the force of buoyancy on it. (Given, )
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