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NCERT Solutions for class 11 Physics | Chapter 8 - Gravitation

Questions
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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