CBSE Class 11 Physics Gravitation MCQs Set C

Question. A remote – sensing satellite of earth revolves in a circular orbit at a height of 0.25 × 10⁶ m above the surface of earth. If earth’s radius is 6.38 × 10⁶ m and g = 9.8 ms^–2, then the orbital speed of the satellite is:
(a) 8.56 km s^–1
(b) 9.13 km s^–1
(c) 6.67 km s^–1
(d) 7.76 km s^–1
Answer: d

Question. If there were a small gravitational effect, then which of the following forces will undergo a change?
(a) Viscous force
(b) Electrostatic force
(c) Magnetic force
(d) Archimedes’ uplift
Answer: b

Question. A satellite S is moving in an elliptical orbit around the earth. The mass of the satellite is very small compared to the mass of the earth. Then,
(a) the total mechanical energy of S varies periodically with time.
(b) the linear momentum of S remains constant in magnitude.
(c) the acceleration of S is always directed towards the centre of the earth.
(d) the angular momentum of S about the centre of the earth changes in direction, but its magnitude remains constant.
Answer: c

Question. Different points in the earth are at slightly different distances from the sun and hence experience different forces due to gravitation. For a rigid body, we know that if various forces act at various points in it, the resultant motion is as if a net force acts on the CM (centre of mass) causing translation and a net torque at the CM causing rotation around an axis through the CM. For the earth-sun system (approximating the earth as a uniform density sphere).
(a) the torque is zero
(b) the torque causes the earth to spin
(c) the rigid body result is not applicable since the earth is not even approximately a rigid body
(d) the torque causes the earth to move around the sun
Answer: a

Question. Satellites orbitting the earth have finite life and sometimes debris of satellites fall to the earth. This is because
(a) the solar cells and batteries in satellites run out
(b) the laws of gravitation predict a trajectory spiralling inwards
(c) of viscous forces causing the speed of satellite and hence height to gradually decrease
(d) of collisions with other satellites
Answer: c

Question. The radius of a planet is twice the radius of earth. Both have almost equal average mass-densities. If V_P and V_E are escape velocities of the planet and the earth, respectively, then
(a) V_E = 1.5V_P
(b) VP = 1.5V_E
(c) V_P = 2V_E
(d) V_E = 3V_P
Answer: c

Question. As observed from the earth, the sun appears to move in an approximate circular orbit. For the motion of another planet like mercury as observed from the earth, this would
(a) be similarly true
(b) not be true because the force between the earth and mercury is not inverse square law
(c) not be true because the major gravitational force on mercury is due to the sun
(d) not be true because mercury is influenced by forces other than gravitational force
Answer: c

Question. Kepler’s third law states that square of period of revolution (T) of a planet around the sun, is proportional to third power of average distance r between sun and planet i.e. T² = Kr³ here K is constant. If the masses of sun and planet are M and m respectively then as per Newton’s law of gravitation force of attraction between them is F = GMm,/r² here G is gravitational constant. The relation between G and K is described as
(a) GMK = 4π²
(b) K = G
(c) K = 1/G
(d) GK = 4π²
Answer: a

Question. A particle of mass M is situated at the centre of a spherical shell of same mass and radius a. The gravitational potential at a point situated at α/2 distance from the centre, will be
(a) -(3GM/a)
(b) -(2GM/a)
(c) -(GM/a)
(d) -(4GM/a)
Answer: a

Question. The ratio of escape velocity at earth (v_e) to the escape velocity at a planet (v_p) whose radius and mean density are twice as that of earth is :
(a) 1 : 2
(b) 1 : 2 √2
(c) 1 : 4
(d) 1 : 2
Answer: b

Question. A black hole is an object whose gravitational field is so strong that even light cannot escape from it. To what approximate radius would earth (mass = 5.98 × 10²⁴ kg) have to be compressed to be a black hole?
(a) 10^{– 9} m
(b) 10^{– 6} m
(c) 10^{– 2} m
(d) 100 m
Answer: c

Question. wo spherical bodies of mass M and 5M and radii R and 2R respectively are released in free space with initial separation between their centres equal to 12 R. If they attract each other due to gravitational force only, then the distance covered by the smaller body just before collision is
(a) 2.5 R
(b) 4.5 R
(c) 7.5 R
(d) 1.5 R
Answer: c

Question. For a satellite moving in an orbit around the earth, the ratio of kinetic energy to potential energy is
(a) 1/2
(b) 1/√2
(c) 2
(d) √2
Answer: a

Question. Both the earth and the moon are subject to the gravitational force of the sun. As observed from the sun, the orbit of the moon
(a) will be elliptical
(b) will not be strictly elliptical because the total gravitational force on it is not central
(c) is not elliptical but will necessarily be a closed curve
(d) deviates considerably from being elliptical due to influence of planets other than the earth
Answer: b

Question. The earth is an approximate sphere. If the interior contained matter which is not of the same density everywhere, then on the surface of the earth, the acceleration due to gravity
(a) will be directed towards the centre but not the same everywhere
(b) will have the same value everywhere but not directed towards the centre
(c) will be same everywhere in magnitude directed towards the centre
(d) cannot be zero at any point
Answer: d

Question. The acceleration due to gravity at a height 1 km above the earth is the same as at a depth d below the surface of earth. Then
(a) d = 1 km
(b) d = (3/2) km
(c) d = 2 km
(d) d = (1/2) km
Answer: c

Question. The density of a newly discovered planet is twice that of earth. The acceleration due to gravity at the surface of the planet is equal to that at the surface of the earth. If the radius of the earth is R, the radius of the planet would be
(a) ½ R
(b) 2 R
(c) 4 R
(d) 1/4 R
Answer: a

Question. The radii of circular orbits of two satellites A and B of the earth, are 4R and R, respectively. If the speed of satellite A is 3 V, then the speed of satellite B will be
(a) 3 V/4
(b) 6 V
(c) 12 V
(d) 3 V/2
Answer: b

Question. The escape velocity from a planet is ve. A tunnel is dug along a diameter of the planet and a small body is dropped into it at the surface. When the body reaches the centre of the planet, its speed will be
(a) v_e
(b) e_v/√2
(c) v_e/2
(d) zero
Answer: b

Question. If the radius of the earth were to shrink by one per cent, its mass remaining the same, the acceleration due to gravity on the earth’s surface would
(a) decrease
(b) remain unchanged
(c) increase
(d) None of these
Answer: c

Question. A cavity of radius R/2 is made inside a solid sphere of radius R. The centre of the cavity is located at a distance R/ 2 from the centre of the sphere. The gravitational force on a particle of mass ‘m’ at a distance R/2 from the centre of the sphere on the line joining both the centres of sphere and cavity is – (opposite to the centre of gravity) [Here g = GM/R², where M is the mass of the sphere]
(a) mg/2
(b) 3mg/8
(c) mg/16
(d) None of these
Answer: b

Question. Imagine a new planet having the same density as that of earth but it is 3 times bigger than the earth in size. If the acceleration due to gravity on the surface of earth is g and that on the surface of the new planet is g’, then
(a) g’ = g/9
(b) g’ = 27g
(c) g’=9g
(d) g’=3g
Answer: d

Question. Explorer 38, a radio-astronomy satellite of mass 200 kg, circles the Earth in an orbit of average radius 3R/2 where R is the radius of the Earth. Assuming the gravitational pull on a mass of 1 kg at the earth’s surface to be 10 N, calculate the pull on the satellite
(a) 889 N
(b) 89 N
(c) 8889 N
(d) 8.9 N
Answer: a

Question. Choose the wrong option.
(a) Inertial mass is a measure of difficulty of accelerating a body by an external force whereas the gravitational mass is relevant in determining the gravitational force on it by an external mass
(b) That the gravitational mass and inertial mass are equal is an experimental result
(c) That the acceleration due to gravity on the earth is the same for all bodies is due to the equality of gravitational mass and inertial mass
(d) Gravitational mass of a particle like proton can depend on the presence of neighbouring heavy objects but the inertial mass cannot
Answer: d

Question. In our solar system, the inter-planetary region has chunks of matter (much smaller in size compared to planets) called asteroids. They
(a) will not move around the sun, since they have very small masses compared to the sun
(b) will move in an irregular way because of their small masses and will drift away into outer space
(c) will move around the sun in closed orbits but not obey Kepler’s laws
(d) will move in orbits like planets and obey Kepler’s laws
Answer: d

Question. The largest and the shortest distance of the earth from the sun are r1 and r2. Its distance from the sun when it is at perpendicular to the major-axis of the orbit drawn from the sun
(a) (r₁ + r₂ ) / 4
(b) (r₁ + r₂ ) /(r₁ – r₂ )
(c) 2 r₁ r₂ /(r₁ + r₂)
(d) (r₁ + r₂ ) / 3
Answer: c

Question. A satellite is launched into a circular orbit of radius R around the earth. A second satellite is launched into an orbit of radius 1.01 R. The period of second satellite is larger than the first one by approximately
(a) 0.5%
(b) 1.0%
(c) 1.5%
(d) 3.0%
Answer: c

Question. A spherical uniform planet is rotating about its axis. The velocity of a point on its equator is V. Due to the rotation of planet about its axis the acceleration due to gravity g at equator is 1/2 of g at poles. The escape velocity of a particle on the pole of planet in terms of V is
(a) V_e = 2V
(b) V_e = V
(c) V_e = V/2
(d) V_e = √3V
Answer: a

Question. At what height from the surface of earth the gravitational potential and the value of g are –5.4 × 10⁷ J kg^–1 and 6.0 ms^–2 respectively ?
Take the radius of earth as 6400 km :
(a) 2600 km
(b) 1600 km
(c) 1400 km
(d) 2000 km
Answer: a

Question. If g_E and g_M are the accelerations due to gravity on the surfaces of the earth and the moon respectively and if Millikan’s oil drop experiment could be performed on the two surfaces, one will find the ratio
electronic charge on the moon/electronic charge on the earth, to be
(a) g_M / g_E
(b) 1
(c) 0
(d) g_E / g_M
Answer: b

 Question. The earth is assumed to be sphere of radius R. A platform is arranged at a height R from the surface of Earth. The escape velocity of a body from this platform is kv, where v is its escape velocity from the surface of the earth. The value of k is
(a) 1/√2
(b) 1/3
(c) 1/2
(d) √2
Answer: a

Question. A ball is dropped from a satellite revolving around the earth at height of 120 km. The ball will
(a) continue to move with same speed along a straight
line tangentially to the satellite at that time
(b) continue to move with same speed along the original orbit of satellite.
(c) fall down to earth gradually
(d) go far away in space
Answer: b

Question. Two identical geostationary satellites are moving with equal speeds in the same orbit but their sense of rotation brings them on a collision course. The debris will
(a) fall down
(b) move up
(c) begin to move from east to west in the same orbit
(d) begin to move from west to east in the same orbit
Answer: a

Question. A planet moving along an elliptical orbit is closest to the sun at a distance r₁ and farthest away at a distance of r₂. If v₁ and v₂ are the linear velocities at these points respectively, then the ratio v₁/v₂ is
(a) (r₁/r₂)²
(b) r₂/r₁
(c) (r₂/r₁)²
(d) r₁/r₂
Answer: b

Question. Two astronauts are floating in gravitation free space after having lost contact with their spaceship. The two will
(a) move towards each other.
(b) move away from each other.
(c) become stationary
(d) keep floating at the same distance between them.
Answer: a

Question. Two spherical bodies of mass M and 5 M and radii R and 2 R released in free space with initial separation between their centres equal to 12 R. If they attract each other due to gravitational force only, then the distance covered by the smaller body before collision is
(a) 4.5 R
(b) 7.5 R
(c) 1.5 R
(d) 2.5 R
Answer: b