GRAVITATION

MULTIPLE CHOICE QUESTIONS

Choose the correct option:

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 (a)

2. The value of acceleration due to gravity(a) is same on equator and poles (c)is least on equator(b) is least on poles (d) increases from pole to equator (c)

3. The gravitational force between two objects is F. If masses of both objectsare halved without changing distance between them, then the gravitationalforce would become(a) F/4 (b) F/2 (c) F (d) 2 F (a)

4. A boy is whirling a stone tied with a string in an horizontal circular path. Ifthe 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 (c)from the boy

5. An object is put one by one in three liquids having different densities. Theobject floats with 1 2 3 , and 9 11 7 parts of their volumes outside the liquid surface in liquids of densities d1, d2 and d3 respectively. Which of thefollowing statement is correct?(a) d1> d2> d3(b) d1> d2< d3(c) d1< d2> d3(d) d1< d2< d3 (c)

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 (d)

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 (c) 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 (d)

9. Two particles are placed at some distance. If the mass of each of the twoparticles is doubled, keeping the distance between them unchanged, thevalue of gravitational force between them will be(a) 1/4 times (c)1/2 times(b) 4 times (d) unchanged (b)

10. The atmosphere is held to the earth by(a) gravity (c) clouds(b) wind (d) earth’smagnetic field (a)

11. The force of attraction between two unit point masses separated by a unitdistance is called(a) gravitational potential (c)gravitational field(b) acceleration due to gravity (d)universal gravitational constant (d)

12. The weight of an object at the centre of the earth of radius R is(a) zero (c) R times the weight at the surface of the earth(b) infinite (d) 1/R2 times the weight at surface of the earth (a)

13. An object weighs 10 N in air. When immersed fully in water, it weighs only8 N. The weight of the liquid displaced by the object will be(a) 2 N (b) 8N (c) 10 N (d) 12N (a)

14. A girl stands on a box having 60 cm length, 40 cm breadth and 20 cmwidth in three ways. In which of the following cases, pressure exerted bythe 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 (b)

15. An apple falls from a tree because of gravitational attraction between theearth and apple. If F1 is the magnitude of force exerted by the earth on theapple and F2 is the magnitude of force exerted by apple on earth, then(a) F1 is very much greater than F2

(b) F2 is very much greater than F1(c) F1 is only a little greater than F2(d) F1 and F2 are equal (d)

16. The gravitation force between two bodies varies with distance r asa) 1/r b) 1/r²c) r d) r² (b)

17. The earth attracts the moon with a gravitational force of 10²º N. Then the moon attracts the earth with a gravitational force of a) 10ˉ²º N b) 10² Nc) 10²º N d) 10¹º N (c)

18. The value of g at pole is a) greater than the value at the equator (c) equal to the value at the equatorb) less than the value at the equator (d) none of the above (a)

19. A coin and feather are dropped together in a vacuum.a) The coin will reach the ground firstb) The feather will reach the ground firstc) Both the bodies will reach the ground togetherd) The feather will not fall down (c)

20 Newton’s law of gravitation is valid a) on the earth only (c) in the laboratory onlyb) on the moon only (d) every where (d)

21. The acceleration due to gravity is 9.8 m/s² a) much above the earth’s surface (c) deep inside the earth b) near the earth’s surface (d) at the centre of the earth (b)

22. When a body is thrown up the force of gravity isa) in the upward direction (c) zerob) in the downward direction (d) in the horizontal direction (b)

VERY SHORT ANSWER QUESTIONS

1. A body of mass 10 kg is taken to the centre of the earth. What will be its mass there?Ans. 10kg

2. Write the units of ‘g’ and ‘G’.Ans g---ms-2; G----Nm2kg-2

3. Define weight of a body.Ans. Weight is the force by which the body is being pulled towards the centre of the earth.

4. What will be the direction of acceleration due to gravity if the body is thrown vertically upwards?Ans. Downwards.

5. Why does a body weighs more at poles than at equator?Ans As Rp<Re, so gp>ge hence Wp>We 6. State the factors on which up thrust or buoyant force depends.Ans It depends on the nature of the fluid.

SHORT ANSWER TYPE QUESTIONS

1. Why are double tyres provided at the rear wheels of a truck?

Ans As pressure =1/Area, so more is the area of tyres lesser is the pressure exerted on the road.

2. Two bodies A and B, having mass 50 kg and 100 kg respectively. They are dropped from a certain height simultaneously. Which body will reach first on earth surface? Why?

Ans Both will reach the earth surface at the same time, as ‘g’ is independent of mass of the object.

3. There are two kinds of balances i.e., a beam balance and a spring balance. If both the balances give the same measure of a given body on the surface of the earth, will they give the same measure on surface of the moon ? Explain. Ans. No, they will not give the same measure, as the g on moon is 1/6th to that on earth so

weight on moon is 1/6th to that on earth.(W=mg)

Across: 5. Gravitational Constant, 6.Tangent, 7.centripetal forceDown: 1. Weight, 2. Gravity, 3. Mass, 4. Gravitational Force.

NUMERICAL QUESTIONS

1. The density of water is 1000 kg/m³ . If the relative density of iron is 7.874, then calculate the density of iron .Ans Density=R.D x Dw so D=7.874 x 1000=7874kg/m3

2. Find the acceleration due to gravity on a planet whose mass is twice and radius is thrice as that of earth .

Ans. gp = 2/9 ge

3. Suppose an astronaut lands on the surface of moon and drops an object from a height of ‘h’ from the surface. Find ‘h’ if the object takes 3s to reach the moon’s surface .Ans h= ut+1/2gmt2

= 0+1/2x9.8/6x32

= 7.35m

Worksheet #2

Topic : Newton’s law of gravitationAssessment Technique :Sorting out based worksheetAssessment parameters :1 mark for each correct abacus beadAssessment time: 10 minInstructions :-Some information about gravitational force, acceleration due to Gravity and gravitational constant is given in the box. Match the given information with the above mentioned quantities By filling the correct number in corresponding abacus column Some information may match with more than one abacus column1 GMm/R2

2 Same for all objects on the moon3 Depends on the mass of the object

4 Henery Cavendish5 9.8 m/s2 at the surface of the earth6 Newton7 6.673 x 10-11Nm2/kg2

8 Decreases with increase in height9 Remains same all over the universe10 Directly proportional to the product of masses of the two objects

10

8

9 8 6

7 5 3

4 2 1 TOPIC - Gravitational Force G g F