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NCERT Solutions for class 11 Physics | Chapter 8 - Gravitation

(1) Who among the following first gave the experimental velocity of G?
[A] Cavendish
[B] Copernicus
[C] Brook Taylor
[D] none of these
Answer: Cavendish
(2) The value of g at a particular point is 9.8 m/sec² suppose the earth suddenly shrink uniformly to half its present size without losing any mass. The value of g at the same point (assuming that the distance of the point from the centre of the earth does not shrink) will become
[A] 9.8 m/sec²
[B] 4.9 m/sec²
[C] 19.6 m/sec²
[D] 2.45 m/sec²
Answer: 9.8 m/sec²

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(3) A body is projected vertically from the surface of the earth of radius R with velocity equal to half of the escape velocity. The maximum height reached by the body is
[A] R
[B] R/2
[C] R/3
[D] R/4
Answer: R/3
(4) What would be the duration of the year if the distance between the earth and the sun gets doubled?
[A] 1032 days
[B] 129 days
[C] 365 days
[D] 730 days
Answer: 1032 days
(5) The time – period of a satellite of earth is 5 hours. If the separation between the earth and the satellite is increased to 4 times the previous value, the new time – period will become
[A] 10 hours
[B] 20 hours
[C] 40 hours
[D] 80 hours
Answer: 40 hours
(6) If a body of mass m is taken out from a point below the surface of earth equal to half the radius of earth, R, to a height R above the earths surface, then work done on it will be
[A] (5/6) mgR
[B] (6/7) mgR
[C] (7/8) mgR
[D] (8/9) mgR
Answer: (7/8) mgR
(7) A missile is launched with a velocity less than the escape velocity. The sum of its kinetic and potential energy is
[A] Positive
[B] Negative
[C] Zero
[D] may be positive or negative
Answer: Negative
(8) The radius of the earth is 6400 km and g = 10 m/s². In order that a body of 5 kg weighs zero at the equator, the angular speed of the earth is
[A] 1/80 rad /s
[B] 1/400 rad /s
[C] 1/800 rad /s
[D] 1/1600 rad /s
Answer: 1/800 rad /s
(9) A artificial satellite moving in a circular orbit around the earth has a total (kinetic + potential) energy E0. Its potential energy is
[A] 2E0
[B] E0
[C] 1.5 E0
[D] -E0
Answer: 2E0
(10) A body weighs 500 N on the surface of the earth. How much would it weight half way below the surface of the earth?
[A] 1000 N
[B] 500 N
[C] 250 N
[D] 125 N
Answer: 250 N
(11) The escape velocity for a body projected vertically upwards from the surface of the earth is 11 km/s. If the body is projected at an angle of 450 with the vertical, the escape velocity will be
[A] 11/√2 km/s
[B] 11√2 km/s
[C] 2 km/s
[D] 11 km/s
Answer: 11 km/s
(12) If the radius of the earth were to be raise by 1% its mass remaining the same, the acceleration due to gravity on the surface of the earth will
[A] increase by 1%
[B] decrease by 2%
[C] decrease by 1%
[D] increase by 2%
Answer: increase by 2%
(13) The escape velocity of projection from the earth is approximately (R = 6400 km)
[A] 7 km/sec
[B] 112 km/sec
[C] 12.2 km/sec
[D] 1.1 km/sec
Answer: 12.2 km/sec
(14) The mean radius of the earth is R, its angular speed on its own axis is w and the acceleration due to gravity at earths surface is g. The cube of the radius of the orbit of a geo-stationary satellite will be
[A] r²g / w
[B] R²w²/ g
[C] RG w²
[D] R²g / w²
Answer: R²g / w²
(15) The masses of two planets are in the ratio 1 : 2. Their radii are in the ratio 1 : 2. The acceleration due to gravity on the planets are in the ratio.
[A] 1 : 2
[B] 2 : 1
[C] 3 : 5
[D] 5 : 3
Answer: 1 : 2
(16) A satellite S is move in an elliptical orbit around the earth. The mass of the satellite is very small compared to the mass of the earth .
[A] The acceleration of S is always directed towards the centre of the earth.
[B] The angular momentum of S about the centre of the earth changes in direction, but its magnitude remains constant.
[C] The total mechanical energy of S varies periodically with time.
[D] The linear momentum of S remains constant in magnitude.
Answer: The acceleration of S is always directed towards the centre of the earth.
(17) There is no atmosphere on the moon because
[A] it is closer to the earth
[B] it revolves round the earth
[C] it gets light from the sun
[D] the escape velocity of gas molecules is less than their root mean square velocity here
Answer: the escape velocity of gas molecules is less than their root mean square velocity here
(18) A body is projected vertically from the surface of the earth of radius R with velocity equal to half of the escape velocity. The maximum height reached by the body is
[A] R
[B] R/2
[C] R/3
[D] R/4
Answer: R/3
(19) If the distance between the earth and the sun were half its present value, the number of day in a year would have been
[A] 64.5
[B] 129
[C] 182.5
[D] 730
Answer: 129
(20) The atmosphere around the earth is held by
[A] Gravity
[B] Winds
[C] Clouds
[D] None of the above
Answer: Gravity

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