CBSE Class 9 Science Gravitation MCQs Set F

Question. The kinetic energy needed to project a body of mass m from the earth surface (radius R) to infinity is
(a) mgR/2
(b) 2 mgR
(c) mgR
(d) mgR/4
Answer: c

Question. A spherical planet far out in space has a mass M₀ and diameter D₀ . A particle of mass m falling freely near the surface of this planet will experience an acceleration due to gravity which is equal to
(a) GM₀ / D₀
(b) 4mGM₀ / D²₀
(c) 4GM₀ / D²₀
(d) GmM₀ / D²₀
Answer: c

Question. A body of mass m kg. starts falling from a point 2R above the Earth’s surface. Its kinetic energy when it has fallen to a point ‘R’ above the Earth’s surface [R-Radius of Earth, M-Mass of Earth, G-Gravitational Constant]
(a) 1/2 GMm/R
(b) 1/6 GMm/R
(c) 2/3 GMm/R
(d) 1/3 GMm/R
Answer: b

Question. Weight of a body of mass m decreases by 1% when it is raised to height h above the earth’s surface. If the body is taken to a depth h in a mine, change in its weight is
(a) 2% decrease
(b) 0.5% decrease
(c) 1% increase
(d) 0.5% increase
Answer: b

Question. 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: b

Question. The mass of a body is increased 4 fold and mass of other body is increased 16 fold. How should the distance between them be changed to keep the same gravitational force between them?
(a) 4 times
(b) (1/4) times
(c) 8 times
(d) (1/8) times
Answer: c

Question. Acceleration due to gravity on moon is 1/6 of the acceleration due to gravity on earth. If the ratio of densities of earth (p_e) and moon (p_m) is {p_e/p_m} = 5/3 then radius of moon Rm in terms of Re will be 
(a) 5/18 R_e
(b) 1/6 R_e
(c) 3/18 R_e
(d) 1/2√3 R_e
Answer: a

Question. When you put an object on a spring balance, what do you measure?
(a) Weight
(b) Force
(c) Mass
(d) Acceleration
Answer: a

Question. A body of mass m rises to height h = R/5 from the earth's surface, where R is earth's radius. If g is acceleration due to gravity at earth's surface, the increase in potential energy is
(a) mgh
(b) 4/5 mgh
(c) 5/6 mgh
(d) 6/7 mgh 
Answer: c 

 Question. If radius of earth is R then the height ‘h’ at which value of ‘g’ becomes one-fourth is 
(a) R/4
(b) 3R/4
(c) R
(d) R/8
Answer: c

Question. Assuming earth to be a sphere of a uniform density, what is the value of gravitational acceleration in a mine 100 km below the earth’s surface (Given R = 6400 km) 
(a) 2 9.66 m/s²
(b) 2 7.64 m/s²
(c) 5.06 m/s²
(d) 2 3.10 m/s²
Answer: a

Question. The mass and diameter of a planet have twice the value of the corresponding parameters of earth. Acceleration due to gravity on the surface of the planet is
(a) 9.8 m / sec²
(b) 4.9 m / sec²
(c) 980m / sec²
(d) 19.6 m / sec²
Answer: b

Question. A body of mass m is placed on the earth’s surface. It is taken from the earth’s surface to a height h = 3R . The change in gravitational potential energy of the body is
(a) 2/3 mgR
(b) 3/4 mgR
(c) mgR / 2
(d) mgR / 4
Answer: b

Question. The acceleration of a body due to the attraction of the earth (radius R) at a distance 2 R from the surface of the earth is (g = acceleration due to gravity at the surface of the earth)
(a) g/9
(b) g/2
(c) g/4
(d) g
Answer: a

Question. In some region, the gravitational field is zero. The gravitational potential in this region 
(a) Must be variable
(b) Must be constant
(c) Cannot be zero
(d) Must be zero
Answer: b

Question. Acceleration due to gravity 'g' for a body of mass 'm' on earth's surface is proportional to (Radius of earth=R,mass of earth=M) 
(a) GM / R²
(b) m°
(c) mM
(d) 1 / R^3/2
Answer: a

Question. The angular velocity of the earth with which it has to rotate so that acceleration due to gravity on 60o latitude becomes zero is (Radius of earth = 6400 km. At the poles g = 10 ms^-2) 
(a) 2.5 x 10^-3 rad/s 
(b) 5.0 x 10^-1 rad/s 
(c) 10 x 10¹ rad/ s 
(d) 7.8 x 10^-2 rad/s
Answer: a

Question. v_e and v_p denotes the escape velocity from the earth and another planet having twice the radius and the same mean density as the earth. Then 
(a) v_e = v_p
(b) v_e = v_p/2
(c) v_e = 2v_p
(d) v_e = v_p/4
Answer: b

Question. The escape velocity of a sphere of mass m from earth having mass M and radius R is given by
(a) √2GM/R 
(b) 2√GM/R
(c) √2GMm/R
(d) √GM/R
Answer: a

Question. In a gravitational field, at a point where the gravitational potential is zero 
(a) The gravitational field is necessarily zero
(b) The gravitational field is not necessarily zero
(c) Nothing can be said definitely about the gravitational field
(d) None of these
Answer: a

Question. Gravitational mass is proportional to gravitational
(a) Field
(b) Force
(c) Intensity
(d) All of these
Answer: d

Question. The diameters of two planets are in the ratio 4 : 1 and their mean densities in the ratio 1 : 2. The acceleration due to gravity on the planets will be in ratio
(a) 1 : 2
(b) 2 : 3
(c) 2 : 1
(d) 4 : 1
Answer: c

Question. If g is the acceleration due to gravity at the earth's surface and r is the radius of the earth, the escape velocity for the body to escape out of earth's gravitational field is
(a) gr
(b) √2gr
(c) g / r
(d) r / g
Answer: b

Question. The escape velocity for a rocket from earth is 11.2 km/sec. Its value on a planet where acceleration due to gravity is double that on the earth and diameter of the planet is twice that of earth will be in km/sec
(a) 11.2
(b) 5.6
(c) 22.4
(d) 53.6
Answer: c

Question. As we go from the equator to the poles, the value of g 
(a) Remains the same
(b) Decreases
(c) Increases
(d) Decreases upto a latitude of 45°
Answer: c 

Question. Escape velocity on a planet is e v . If radius of the planet remains same and mass becomes 4 times, the escape velocity becomes 
(a) e 4 v
(b) e 2 v
(c) e v
(d) e v21
Answer: b

Question. The mass of the earth is 81 times that of the moon and the radius of the earth is 3.5 times that of the moon. The ratio of the escape velocity on the surface of earth to that on the surface of moon will be
(a) 0.2
(b) 2.57
(c) 4.81
(d) 0.39
Answer: c

Question. The change in potential energy, when a body of mass m is raised to a height nR from the earth's surface is (R = Radius of earth) 
(a) mgR n/n-1
(b) nmgR
(c) mgR n²/n²+ 1
(d) mgR n/n+ 1
Answer: d

Question. Two planets of radii in the ratio 2 : 3 are made from the material of density in the ratio 3 : 2. Then the ratio of acceleration due to gravity g₁ / g₂ at the surface of the two planets will be 
(a) 1
(b) 2.25
(c) 4/9
(d) 0.12
Answer: a

Question. The radius of the earth is 6400 km and 2 g = 10m / sec². In order that a body of 5 kg weighs zero at the equator, the angular speed of the earth is 
(a) 1/80 radian/sec
(b) 1/400 radian/sec
(c) 1/800 radian/sec
(d) 1/1600 radian/sec
Answer: c 

Question. Gas escapes from the surface of a planet because it acquires an escape velocity. The escape velocity will depend on which of the following factors :
I. Mass of the planet Gravitation
II. Mass of the particle escaping
III. Temperature of the planet
IV. Radius of the planet
Select the correct answer from the codes given below :
(a) I and II
(b) II and IV
(c) I and IV
(d) I, III and IV
Answer: c