CBSE Class 9 Science Gravitation Sure Shot Questions

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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 , 2/11,  and  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

(b) 4 times

(c) 1/2times

(d) unchanged

10. The earth attracts a body of mass 2 kg on its surface with a force of
(a) 9.8 N

(b) 19.6 N

(c) 6.67 x 10^–11 N

(d) 2 x 6.67 x 10^–11 N

11. A stone dropped from a building takes 4 s to reach the ground. The height of the building is

(a) 19.6 m

(b) 80.4 m

(c) 78.4 m

(d) 156.8 m

12. If ge is acceleration due to gravity on earth and gm is acceleration due to gravity on moon, then

(a) ge = gm

(b) ge < gm

(c) ge = 1/6gm

(d) gm = 1/6ge

13. The mass of a body on the surface of earth is 12 kg. If acceleration due to gravity on moon is 1/6 of acceleration due to gravity on earth, then its mass on moon will be

(a) 2 kgf

(b) 72 kg

(c) 12 kg

(d) zero

14. The atmosphere is held to the earth by

(a) gravity

(b) wind

(c) clouds

(d) earth’s magnetic field

15. 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

16. 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/^R2 times the weight at surface of the earth

SHORT ANSWER QUESTIONS

17. What is the source of centripetal force that a planet requires to revolve around the Sun? On what factors does that force depend?

18. 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?

19. Suppose gravity of earth suddenly becomes zero, then in which direction will the moon begin to move if no other celestial body affects it?

20. 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.

21. 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?

22. Calculate the average density of the earth in terms of g, G and R.

23. The earth is acted upon by gravitation of Sun, even though it does not fall into the Sun. Why?

24. Calculate the density of Earth from Newton’s law of gravitation.

25. A body weighs more at poles than at the equator of earth. Why?

26. Two particles of equal mass(m) move in a circle of radius (r) under the action of their mutual gravitational attraction. Find the speed of each particle.

LONG ANSWER QUESTIONS

27. 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?

28. 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.

29. 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.

30. Distinguish between mass and weight. Show that mass of a body numerically equal to weight of the body except at the centre of earth.

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