CBSE Class 9 Science Gravitation MCQs Set 05

Question. A man can jump to a height of 1.5 m on a planet A. What is the height he may be able to jump on another planet whose density and radius are, respectively, one-quarter and one-third that of planet A
(a) 1.5 m
(b) 15 m
(c) 18 m
(d) 28 m
Answer: c

Question. At what height over the earth's pole, the free fall acceleration decreases by one percent (assume the radiusof earth to be 6400 km) 
(a) 32 km
(b) 80 km
(c) 1.253 km
(d) 64 km
Answer: a

 Question. A body is projected vertically upwards from the surface of a planet of radius R with a velocity equal to half the escape velocity for that planet. The maximum height attained by the body is 
(a) R/3
(b) R/2
(c) R/4
(d) R/5
Answer: a 

Question. The moon's radius is 1/4 that of the earth and its mass is 1/80 times that of the earth. If g represents the acceleration due to gravity on the surface of the earth, that on the surface of the moon is 
(a) g/4
(b) g/5
(c) g/6
(d) g/8
Answer: b

Question. What is the intensity of gravitational field of the centre of a spherical shell 
(a) Gm/r²
(b) g
(c) Zero
(d) None of these
Answer: c

Question. Let g be the acceleration due to gravity at earth's surface and K be the rotational kinetic energy of the earth.
Suppose the earth's radius decreases by 2% keeping all other quantities same, then
(a) g decreases by 2% and K decreases by 4%
(b) g decreases by 4% and K increases by 2%
(c) g increases by 4% and K increases by 4%
(d) g decreases by 4% and K increases by 4%
Answer: c

Question. A body weight 500 N on the surface of the earth. How much would it weigh half way below the surface of the earth
(a) 125 N
(b) 250 N
(c) 500 N
(d) 1000 N
Answer: b

Question. If the earth rotates faster than its present speed, the weight of an object will 
(a) Increase at the equator but remain unchanged at the poles
(b) Decrease at the equator but remain unchanged at the poles
(c) Remain unchanged at the equator but decrease at the poles
(d) Remain unchanged at the equator but increase at the poles
Answer: b

Question. Radius of orbit of satellite of earth is R. Its kinetic energy is proportional to 
(a) 1/R
(b) 1/√R
(c) R
(d) 1/R^3/2
Answer: a

Question. The universal constant of gravitation G has the unit
(a) N
(b) m/s²
(c) (N m²)/kg²
(d) J
Answer: b

Question. Where will it be profitable to purchase one kilogram sugar?
(a) At poles
(b) At equator
(c) At 45c latitude
(d) at 40c latitude
Answer: b

Question. The gravitational potential energy of a body of mass ‘m’ at the earth’s surface -mgR_e . Its gravitational potential energy at a height R_e from the earth’s surface will be (Here e R is the radius of the earth)
(a) -2 mgR_e
(b) 2 mgR_e
(c) 1/2 mgR_e
(d) -1/2 mgR_e
Answer: d

Question. R is the radius of the earth and ϖ is its angular velocity and p g is the value of g at the poles. The effective value of g at the latitude λ = 60° will be equal to
(a) g_p - 1/4 R²ϖ
(b) g_p - 3/4 R²ϖ
(c) g_p - R²ϖ
(d) g_p + 1/4 R²ϖ
Answer: a

 Question. R and r are the radii of the earth and moon respectively. p_e and p_m are the densities of earth and moon respectively. The ratio of the accelerations due to gravity on the surfaces of earth and moon is 
(a) R/r p_e/p_m
(b) r/R p_e/p_m
(c) r/R p_m/p_e
(d) R/r p_e/p_m
Answer: a

Question. Weight of 1 kg becomes 1/6 on moon. If radius of moon is 1.768 x 10⁶ m , then the mass of moon will be 
(a) 1.99 x 10³⁰ kg
(b) 7.56 x 10²² kg 
(c) 5.98 x 10²⁴ kg 
(d) 7.65 x 10²² kg
Answer: d

Question. The gravitational force between two point masses m₁ and m₂ at separation r is given by F = k m₁m₂ / r₂
The constant k 
(a) Depends on system of units only
(b) Depends on medium between masses only
(c) Depends on both (a) and (b)
(d) Is independent of both (a) and (b) 
Answer: a

Question. The acceleration due to gravity is g at a point distant r from the centre of earth of radius R. If r < R , then
(a) g ∝ r
(b) g ∝ r²
(c) g ∝ r^-1
(d) g ∝ r^-2
Answer: a

Question. Mass of moon is 7.34 x 10²² kg. If the acceleration due to gravity on the moon is 1.4 m / s² , the radius of the moon is
(G = 6.667 10^-11 Nm² / kg² )
(a) 0.56 x 10⁴ m
(b) 1.87 x 10⁶ m
(c) 1.92 x 10⁶ m
(d) 1.01 x 10⁸ m
Answer: b

Question. What should be the velocity of earth due to rotation about its own axis so that the weight at equator become 3/5 of initial value. Radius of earth on equator is 6400 km
(a) 7.4 10^-4 rad / sec 
(b) 6.7 10^-4 rad / sec 
(c) 7.8 10^-4 rad / sec
(d) 8.7 10^-4 rad / sec
Answer: c

Question. At the surface of a certain planet, acceleration due to gravity is one-quarter of that on earth. If a brass ball is transported to this planet, then which one of the following statements is not correct
(a) The mass of the brass ball on this planet is a quarter of its mass as measured on earth
(b) The weight of the brass ball on this planet is a quarter of the weight as measured on earth
(c) The brass ball has the same mass on the other planet as on earth
(d) The brass ball has the same volume on the other planet as on earth 
Answer: a

Question. If the mass of earth is 80 times of that of a planet and diameter is double that of planet and ‘g’ on earth is 9.8m/s² , then the value of ‘g’ on that planet is 
(a) 4.9m/s²
(b) 0.98m/s²
(c) 0.49m/s²
(d) 49m/s²
Answer: c

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 acceleration due to gravity at the surface of the moon to that at the surface of the earth is 
(a) 0.15
(b) 0.04
(c) 1
(d) 6  
Answer: a

Question. A rocket is launched with velocity 10 km/s. If radius of earth is R, then maximum height attained by it will be
(a) 2R
(b) 3R
(c) 4R
(d) 5R
Answer: c

Question. There are two bodies of masses 100 kg and 10000 kg separated by a distance 1 m. At what distance from the smaller body, the intensity of gravitational field will be zero
(a) 1/9 m
(b) 1/10 m
(c) 1/11 m
(d) 10/11 m
Answer: c

Question. The acceleration due to gravity near the surface of a planet of radius R and density d is proportional to
(a) d/R²
(b) dR²
(c) dR
(d) d/R 
Answer: c

Question. Gravitational force is the
(a) weakest force
(b) strongest force
(c) short-range force
(d) non-central force
Answer: a

Question. Energy required to move a body of mass m from an orbit of radius 2R to 3R is
(a) GMm/12R²
(b) GMm/3R² 
(c) GMm/8R
(d) GMm/6R
Answer: d

Question. If the radius of the earth shrinks by 1.5% (mass remaining same), then the value of acceleration due to gravity changes by 
(a) 1%
(b) 2%
(c) 3%
(d) 4%
Answer: c

Question. Radius of earth is around 6000 km. The weight of body at height of 6000 km from earth surface becomes
(a) Half
(b) One-fourth
(c) One third
(d) No change
Answer: b

Question. Choose the correct statement from the following : 
Weightlessness of an astronaut moving in a satellite is a situation of
(a) Zero g
(b) No gravity
(c) Zero mass
(d) Free fall
Answer: d

Question. An object weights 72 N on earth. Its weight at a height of R/2 from earth is 
(a) 32 N
(b) 56 N
(c) 72 N
(d) Zero
Answer: a 

Question. If mass of a body is M on the earth surface, then the mass of the same body on the moon surface is
(a) M/6
(b) Zero
(c) M
(d) None of these
Answer: c

Question. The escape velocity from the earth is about 11 km/second. The escape velocity from a planet having twice the radius and the same mean density as the earth, is
(a) 22 km/sec
(b) 11 km/sec
(c) 5.5 km/sec
(d) 15.5 km/sec
Answer: a

Question. 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 depending upon its initial velocity 
Answer: b 

Question. What is the unit of relative density?
(a) kg m³
(b) kg/m³
(c) per m³
(d) It is unitless
Answer: 

Question. A body weight W newton at the surface of the earth. Its weight at a height equal to half the radius of the earth will be
(a) W/2
(b) 2W/3
(c) 4W/9
(d) 8W/27
Answer: c

Question. The gravitational field due to a mass distribution is E = K / x³ in the x-direction. (K is a constant). Taking the gravitational potential to be zero at infinity, its value at a distance x is 
(a) K/x
(b) K/2x
(c) K / x²
(d) K / 2x²
Answer: d

Question. A particle falls towards earth from infinity. It’s velocity on reaching the earth would be 
(a) Infinity
(b) √2gR
(c) 2√gR
(d) Zero 
Answer: b

Question. At what height from the ground will the value of ‘g’ be the same as that in 10 km deep mine below the surface of earth
(a) 20 km
(b) 10 km
(c) 15 km
(d) 5 km
Answer: a

Question. Escape velocity of a body of 1 kg mass on a planet is 100 m/sec. Gravitational Potential energy of the body at the Planet is 
(a) – 5000 J
(b) – 1000 J
(c) – 2400 J
(d) 5000 J
Answer: a

Question. The value of ‘g’ at a particular point is 2 9.8 m / s² . Suppose the earth suddenly shrinks 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 earth does not shrink) will now be Gravitation
(a) 2 4.9 m / sec²
(b) 2 3.1m / sec²
(c) 2 9.8 m / sec²
(d) 2 19.6 m / sec²
Answer: c

Question. At what altitude in metre will the acceleration due to gravity be 25% of that at the earth's surface (Radius ofearth = R metre) 
(a) 1/4 R
(b) R
(c) 3/8
(d) R/2
Answer: b

Question. If the angular speed of the earth is doubled, the value of acceleration due to gravity (g) at the north pole
(a) Doubles
(b) Becomes half
(c) Remains same
(d) Becomes zero
Answer: c