# Class 9 Physics Gravitation v. The altitude of geostationary orbits in which communication satellites are launched above the surface of the Earth is:(a) 850 \mathrm{~km} (b) 1000 \mathrm{~km} (c) 6400 \mathrm{~km} (d) 42300

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##### v. The altitude of geostationary orbits in which communication satellites are launched above the surface of the Earth is:(a) 850 \mathrm{~km} (b) 1000 \mathrm{~km} (c) 6400 \mathrm{~km} (d) 42300 \mathrm{~km}

6. At what distance from the centre of the earth does the gravitational acceleration have one half the value that It has on the earths surface?

2. A hoop and disc have same mass and radius. Their rotational K.E are related by an equation.a) K . E_{\text {hoop }}=K . E_{\text {disc }} b) K . E_{\text {hoop }}=2 K . E_{\text {disc }} c) K . E_{\text {hoop }}=1 / 2 K . E_{\text {disc }} d) K . E_{\text {hoop }}=4 K . E_{\text {disc }}

23. A cyclist cycling around a circular racing track skids becausea) The centripetal force upon him is less than limiting frictionb) The centripetal force upon him is greater than limiting frictionc) The centripetal force upon him is equal to the limiting frictiond) The friction between the tyres of the cycle and road vanishes

45. The value of gravitational constant was determined bya) Newtonb) Keplerc) Cavendishd) Maxwell

5. Radius of geo-stationary orbit form center of earth is nearly.a) 42000 \mathrm{~km} b) 36000 \mathrm{~km} c) 24000 \mathrm{~km} d) 18000 \mathrm{~km}

40. The sun exerts a forces of attraction on the planets for keeping them in theira) Axesb) Spin-motionc) Orbitsd) None of them

5.6 Find the value of g due to the Earth at geostationary satellite. The radius of the geostationary orbit is 48700 \mathrm{~km} . \left(0.17 \mathrm{~ms}^{-2}\right)

6. According to Einstein the gravity interaction is possible between.a) Material objects onlyb) Material objects and electromagnetic radiation onlyc) Electromagnetic radiations.d) None of the above.

26. Angular speed of seconds hand of a watch in \mathrm{rad}^{-1} is.a) \pi b) \pi / 2 c) \pi / 30 d) \pi / 180

18. If a car moves with a uniform speed of 2 \mathrm{~ms}^{-1} in a circle of radius 0.4 . its angular speed is.a) 4 \mathrm{rad} \mathrm{s}^{-1} b) 5 \mathrm{rad} \mathrm{s}^{-1} c) 1.6 \mathrm{rad} \mathrm{s}^{-1} d) 2.8 \mathrm{rad} \mathrm{s}^{-1}

7. The period of a circular motion is given by.a) T=r V b) T=\omega w c) T=2 \pi \omega d) T=2 \pi / \omega

54. At what depth below the earth surface the value of g reduces to one half of its value on the earths surfacea) R_{e} / 2 b) R_{e} / 4 c) R_{e} d) 2 R_{e}

2 Fil in the blanks(a) The moon revolves around the earth due to the presence of between the earth and moon.

5.5 Calculate the value of \mathrm{g} at a height of 3600 \mathrm{~km} above the surface of the Earth. \left(4.0 \mathrm{~ms}^{-2}\right)

2. Once value of \mathrm{G} has been measured in the laboratory. how it can be used to determine the mass of the earth. Explain.

1 Whether true or false If false correct the following:f. If the cable carrying the elevator breaks the elevator will g 0 up with an acceleration equal to \mathrm{g} .

5.16 On what factors the orbital speed of a satellite depends?

1 Whether true or false If false correct the following:a. Every body in the universe repels every other body with a force which is inversely proportional to the product of their masses.b. The force of gravitational attraction is directly proporti. onal to the square of the distance between two bodies.c. The force with which the earth-repels a body on Its surface towards its centre is equal to its weight.d. The value of \mathrm{g} increases with the increase of thz di tance of the body from the centre of earth.e. Gravitational force is of a very large order of about 6.67 \times 10^{-11} \mathrm{Nm}^{2} / \mathrm{kg}^{2} .f. If the cable carrying the elevator breaks the elevator will go up with an acceleration equal to g .

5.3 Do you attract the Earth or the Earth attracts you? Which one is attracting with a larger force? You or the Earth.

2 Fil in the blanks(a) The moon revolves around the earth due to the presence of ......... between the earth and moon.(b) The force of attraction acts along the .... joining the two Interacting bodies.(c) The pull of the earth on any body above the surface of the earth ......... as the distance from the centre of the the earth decreases.(d) The value of \mathrm{g} is .... of the mass of th. falling body towards the earth.(e) Artificlal gravity can be supplied by .... the space craft so that normal force of gravity can be supplied to the passengers.

67. The artificial gravity is created in the satellite toa) Increase the orbital speed of the satelliteb) Keep the satellite in its orbitc) Overcome the weightlessness experienced by the astronautd) Keep the orbital radius of the satellite constant

2 Fil in the blanks(c) The pull of the earth on any body above the surface of the earth \ldots \ldots . . as the distance from the centre of the the earth decreases.

EXAMPLE 5.1 Two lead spheres each of mass 1000 \mathrm{~kg} are kept with their centres 1 \mathrm{~m} apart. Find the gravitational force with which they attract each other.

5.12 Why does the value of g vary from place to place?

4. Geo-stationary satellite completes one rotation around earth in.a) 3 hoursb) 6 hoursc) 9 hoursd) 24 hours

5.7 The value of \mathrm{g} is 4.0 \mathrm{~ms}^{-2} at a distance of 10000 \mathrm{~km} from the centre of the Earth. Find the mass of the Earth. \left(5.99 \times 10^{24} \mathrm{~kg}\right)

1 Whether true or false If false correct the following:a. Every body in the universe repels every other body with a force which is inversely proportional to the product of thelr masses.