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EPP_ Phy_HW.03
EPP(Extra Practice Problem) – HW Assignment 3
Gravitation
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 gravitation force
would become
(a) F/4
(b) F/2
(c) F
(d) 2F
4. A boy is whirling a stone tied with a string in a horizontal circular path the
string breaks, the stone
(a) will continue to move in the circular path
(b) will move along a straight line towards the center 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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Std 9 EPP www.AhaGuru.com
Balaji Sampath
EPP_ Phy_HW.03
5. 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.
6. 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.
7. 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.
8. 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
9. The atmosphere is held to the earth by
(a) gravity
(b) wind
(c) clouds
(d) earth’s magnetic field
10. 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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Std 9 EPP www.AhaGuru.com
Balaji Sampath
EPP_ Phy_HW.03
11. The weight of an object at the center of the earth of radius R is
(a) zero
(b) infinite
(c) R times the weight at the surface of the earth
(d) 1/R2 times the weight at surface of the earth.
12. An apple falls from a tree because of gravitational attraction between the
earth and apple. If F1 is the magnitude of force exerted by the earth on the
apple and F2 is the magnitude of force exerted by apple on earth, then
Short answers
13. What is the source of centripetal force that a planet requires to revolve
around the sun? On what factors does that force depend?
14. 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?
15. Suppose gravity of earth suddenly becomes zero, then in which direction
will the moon begin to move if no other celestial body affects it?
16. 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.
17. 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?
18. Calculate the average density of earth in terms of g, G, m?
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Std 9 EPP www.AhaGuru.com
Balaji Sampath
EPP_ Phy_HW.03
19. The earth is acted upon by gravitation of sun, even though it does not fall
into the sun. Why?
20. 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?
21. How does the force of attraction between 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 this hypothesis or not? Comment.
22. 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?
a. one of the objects is hollow and the other one is solid and
b. both of them are hollow, size remaining the same in each case. Give reason.
