Infinite Pi Academy
Question bank – 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
2. 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
3. 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) 2 F
4. 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
5. An object is put one by one in three liquids having different densities. The object floats with 1/9, 2/11and 3/7
parts of their volumes outside the liquid surface in liquids of densities d1, d2 and d3 respectively. Which of the
following statement is correct? (a) d1> d2> d3 (b) d1> d2< d3 (c) d1< d2> d3 (d) d1< d2< d3
6. In the relation F = (G M m)/d2, 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
7. Law of gravitation gives the gravitational force between (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
8. The value of quantity G in the law of gravitation (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
9. Two particles are placed at some distance. If the mass of each of the two particles is doubled, keeping the distance
between them unchanged, the value of gravitational force between them will be (a) 1/4 times (b) 4 times (c) 1/2
times (d) unchanged
10. The atmosphere is held to the earth by (a) gravity (b) wind (c) clouds (d) earth’s magnetic field
11. 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
12. 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) 1/R^2 times the weight at surface of the earth
Long answers.
1.How does the force of gravitation between two objects change when the distance between them is reduced to half
2.Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster
than a light object?
3.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 × 10^24 kg and radius of the earth is 6.4 × 10^6 m.)
4.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?
5.If the moon attracts the earth, why does the earth not move towards the moon?
6.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?
7.What is the importance of universal law of gravitation?
8.What is the acceleration of free fall? 9. What do we call the gravitational force between the earth and an object?
9.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.]
10.Why will a sheet of paper fall slower than one that is crumpled into a ball?
11.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 newtons of a 10 kg object on the moon and on the earth?
12.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.
13.A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the
ground.
14.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?
15.Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 10^24 kg
and of the Sun = 2 × 10^30 kg. The average distance between the two is 1.5 × 10^11 m.
16.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. Calculate when and where the two stones will meet.
17.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.
18.What is the source of centripetal force that a planet requires to revolve around the Sun? On what factors does
that force depend?
19.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?
20.Suppose gravity of earth suddenly becomes zero, then in which direction will the moon begin to move if no other
celestial body affects it?
21.Identical packets are dropped from two aeroplanes, 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.
22.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?
23.Calculate the average density of the earth in terms of g, G and R. (b).The earth is acted upon by gravitation of Sun,
even though it does not fall into the Sun. Why?
24.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?
25.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. (b)Two objects of masses m1 and m2 having the same size are dropped
simultaneously from heights h1 and h2 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.
26.(a) 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. (b)
A ball weighing 4 kg of density 4000 kg m–3 is completely immersed in water of density 10^3 kg m–3. Find the force
of buoyancy on it. (Given g = 10 m s–2.)
