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question_answer1) Why is the law of gravitation called the universal law?
question_answer2) Why is G called the universal gravitational constant?
question_answer3) What is the ratio of the force of attraction between two bodies kept in air and the same distance apart in water?
question_answer4) If spheres of same material and same radius r are touching each other, then show that the gravitational force between them is directly proportional to \[{{r}^{\mathbf{4}}}\].
question_answer5) If the density of planet is doubled without any change in its radius, how does \[g\] change on the planet?
question_answer6) Is it possible to shield a body from gravitational effects?
question_answer7) If the force of gravity acts on all bodies in proportion to their masses, why does a heavy body not fall faster than a light body?
question_answer8) The mass of the moon is nearly 10% of the mass of the earth. What will be the gravitational force of the earth on the moon, in comparison to the gravitational force of the moon on the earth?
question_answer9) Earth is continuously pulling the moon towards its centre, still it does not fall to the earth. Why?
question_answer10) We cannot move finger without disturbing all stars. Why?
question_answer11) According to Newton's law of gravitation, the apple and the earth experience equal and opposite forces due to gravitation. But it is the apple that falls towards the earth and not vice-versa. Why?
question_answer12) According to Newton's law of gravitation, every particle of matter attracts every other particle. But bodies on the surface of earth never move towards each other on account of this force of attraction. Why?
question_answer13) Does the gravitational force of attraction of the earth become zero at some height above the earth? Give reason.
question_answer14) Which is more fundamental-mass or weight of a body?
question_answer15) If the diameter of the earth becomes twice its present value but its mass remains unchanged, then how would be the weight of an object on the surface of the earth affected?
question_answer16) If the diameter of the earth becomes half its present value but its average density remains unchanged then how would be the weight of an object on the surface of the earth affected?
question_answer17) The mass and diameter of a planet are twice those of the earth. What will be the time-period of that pendulum on this planet, which is a second's pendulum on the earth?
question_answer18) If the radii of two planets be \[{{R}_{1}}\] and \[{{R}_{2}}\] and their mean densities be \[{{\rho }_{1}}\] and \[{{\rho }_{2}}\], then prove that the ratio of accelerations due to gravity on the planets will be \[{{R}_{1}}{{\rho }_{1}}:{{R}_{2}}{{\rho }_{2}}.\]
question_answer19) The distance between two bodies A and B is r. Taking the gravitational force according to the law of inverse square of r, the acceleration of the body is a. If the gravitational force follows an inverse fourth power law, then what would be the acceleration of the body A?
question_answer20) Why is centre of mass of a body often called its centre of gravity?
question_answer21) Why the value of g is more at the poles than at the equator?
question_answer22) Why a body weighs more at the poles than at the equator?
question_answer23) Where does a body weigh more? At the sea level or on the mountains?
question_answer24) Where will a body weigh more - 1 km above the surface of earth or 1 km below the surface of earth?
question_answer25) Does the concentration of the earth's mass near its centre change the variation of \[\text{g}\] with height compared with a homogeneous sphere? How?
question_answer26) The weight of a body is less inside the earth than on the surface. Why?
question_answer27) Why do you feel giddy while moving on a merry-go-round?
question_answer28) At which place on earth's surface, the value of \[g\] is largest and why?
question_answer29) When dropped from the same height a body reaches the ground quicker at poles than at the equator. Why?
question_answer30) When a clock controlled by a pendulum is taken from the plains to a mountain, it becomes slow but a wrist-watch controlled by a spring remains unaffected. Explain the reason for the difference in the behaviour of the two watches.
question_answer31) A clock fitted with a pendulum and another with a spring indicate correct time on earth. Which shows correct time on the moon?
question_answer32) Why does a tennis ball bounce higher on a hill than on plains?
question_answer33) A man can jump six times as high on the moon as that on the earth. Justify. Or Explain, why one can jump higher on the surface of the moon than that on the earth.
question_answer34) Moon-travellers tie heavy weight at their back before landing on the moon. Why?
question_answer35) Why is earth flat at the poles?
question_answer36) What is the effect of rotation of the earth on the acceleration due to gravity?
question_answer37) Name two factors which determine whether a planet would have an atmosphere or not.
question_answer38) If the earth stops rotating about its axis, what will be the effect on the value of g? Will this effect be same at all places?
question_answer39) If the earth stops rotating about its axis, then by what value will the acceleration due to gravity change at the equator?
question_answer40) Explain why tidal waves (high tide and low tide) are formed on seas.
question_answer41) Why are we not thrown off the surface of the earth by the centrifugal force?
question_answer42) A satellite does not need any fuel to circle around the earth. Why?
question_answer43) Why a multi-stage rocket is required to launch a satellite?
question_answer44) Why do different planets have different escape velocities?
question_answer45) An elephant and an ant are to be projected out of earth into space. Do we need different velocities to do so?
question_answer46) Does a rocket really need the escape velocity of \[\mathbf{11}.\mathbf{2}\text{ }\mathbf{km}{{\mathbf{s}}^{-\mathbf{1}}}\] initially to escape from the earth?
question_answer47) The moon has no atmosphere. Why?
question_answer48) The earth has atmosphere. Why?
question_answer49) Lighter gases like \[{{H}_{2}}\], He, etc. are rare in the atmosphere of the earth. Why?
question_answer50) The gravitational force exerted by the sun on the moon is greater than (about twice as great as) the gravitational force exerted by the earth on the moon. Why then doesn't the moon escape from the earth (during a solar eclipse, for example)?
question_answer51) The escape velocity for a satellite is\[\mathbf{11}.\mathbf{2}\text{ }\mathbf{km}{{\mathbf{s}}^{-1}}\]. If the satellite is launched at an angle of \[\mathbf{60}{}^\circ \] with the vertical, what will be the escape velocity?
question_answer52) An astronaut, while revolving in a circular orbit happens to throw a spoon outside. Will the spoon reach the surface of the earth?
question_answer53) An artificial satellite revolves around the earth without using any fuel. On the other hand, an aeroplane requires fuel to fly. Why?
question_answer54) Why are space rockets usually launched from west to east in the equatorial plane?
question_answer55) A satellite of small mass burns during its descent and not during ascent. Why?
question_answer56) Is it possible to place an artificial satellite in an orbit such that it is always visible over New Delhi?
question_answer57) The astronauts in a satellite orbiting the earth feel weightlessness. Does the weightlessness depend upon the distance of the satellite from the earth? Give reason.
question_answer58) Can we determine the gravitational mass of a body inside an artificial satellite?
question_answer59) A satellite is orbiting the earth with speed \[{{\upsilon }_{0}}\] to make the satellite escape, what should be the minimum percenta8ge increase in its velocity?
question_answer60) Why an astronaut in an orbiting space-craft is not in zero gravity although weightless?
question_answer61) Why does an astronaut in spacecraft feel weightlessness?
question_answer62) Two identical geostationary satellites are moving with equal speeds in the same orbit but their sense of rotation brings them on a collision course. What will happen to the debris?
question_answer63) The linear speed of a rocket is not constant in its orbit. Comment.
question_answer64) Identify the portion of sun in the following diagram if the linear speed of the planet is greater at C compared to that at D.
question_answer65) The largest and shortest distances of the earth from the sun are \[{{r}_{1}}\] and \[{{r}_{2}}\] respectively. What is the distance from the sun when it is perpendicular to the major axis of the orbit from the sun?
question_answer66) Why does the weight of a body become zero at the centre of the earth?
question_answer67) Imagine a spacecraft going from the earth to the moon. How does its weight vary as it goes from the earth to the moon?
question_answer68) The artificial satellite does not have any fuel, but even then it remains in its orbit around the earth. Why.
question_answer69) According to Albert Einstein, no particle can have velocity equal to or greater than that of light. Hence what may be the value of escape velocity from the surface of a 'Black hole' such that it holds everything to itself?
question_answer70) Answer the following : (a) Among the known types of forces in nature, the gravitational force is the weakest. Why then does it play a dominant role for motion of bodies on the terrestrial, astronomical and cosmological scale? (b) Do the forces of friction and other contact forces arise due to gravitational attraction? If not, what is the origin of these forces?
question_answer71) Choose the correct alternatives : (i) If the gravitational potential energy of two mass points infinite distance away is taken to be zero, the gravitational potential energy of a galaxy is (positive/negative/zero). (ii) The universe on the large scale is shaped by (gravitational/electromagnetic) forces, on the nuclear scale by (gravitational/ electromagnetic/ strong nuclear) forces.
question_answer72) What is the difference between inertial mass and gravitational mass of a body?
question_answer73) Which of the following observations point to the equivalence of inertial and gravitational mass: (a) Two spheres of different masses dropped from the top of a long evacuated tube reach the bottom of the tube at the same time. (b) The time-period of a simple pendulum is independent of its mass. (c) The gravitational force on a particle inside a hollow isolated sphere is zero. (d) For a man in closed cabin that is falling freely under gravity, gravity 'disappears'. (e) An astronaut inside a spaceship orbiting around the Earth feels weightless. (f) Planets orbiting around the sun obey Kepler's Third Law (approximately). (g) The gravitational force on a body due to the Earth is equal and opposite to the gravitational force on the Earth due to the body.
question_answer74) A body is taken from the centre of the earth to the moon. What will be the changes in the weight of the body?
question_answer75) Mention the conditions under which the weight of a person can become zero.
question_answer76) How will the value of g be affected if (i) the rotation of the earth stops (ii) the rotational speed of the earth is doubled (iii) the rotational speed of the earth is increased to seventeen times its present value?
question_answer77) When a satellite moves to a lower orbit in the atmosphere of the earth, it becomes hot. This indicates that there is some dissipation in its mechanical energy. But the satellite spirals down towards the earth with an increasing speed, why?
question_answer78) What are the conditions under which a rocket fired from the earth becomes a satellite of the earth and orbits in a circle?
question_answer79) What would happen if the force of gravity were to disappear suddenly?
question_answer80) The radii of two planets are R and \[2R\] respectively and their densities \[\rho \] and \[\rho /2\]respectively. What is the ratio of acceleration due to gravity at their surfaces?
question_answer81) The time period of the satellite of the earth is 5 hours. If the separation between the earth and the satellite is increased to 4 times the previous value, then what will be the new time period of the satellite?
question_answer82) Prove that acceleration due to gravity on the surface of the earth is given by \[g=\frac{4}{3}\pi \rho GR,\], where \[G\] is gravitational constant, \[\rho \] is mean density and R is the radius of the earth.
question_answer83) Why is the weight of a body at the poles more than the weight at the equator? Explain.
question_answer84) Why does the earth impart the same acceleration to all bodies?
question_answer85) If suddenly the gravitational force of attraction between the earth and a satellite revolving around it becomes zero, what will happen to the satellite?
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