CBSE Class 11 Physics Gravitation MCQs Set B

Question: Consider Earth to be a homogeneous sphere. Scientist A goes deep down in a mine and scientist B goes high up in a balloon. The gravitational field measured by
a) A goes on decreasing and that by B goes on increasing
b) B goes on decreasing and that by A goes on increasing
c) each decreases at the same rate
d) each decreases at different rates
Answer: d

Question: The radius of a planet is 1/4th of Re and its acc. due to gravity is 2g. What would be the value of escape velocity on the planet, if escape velocity on earth is ve.
a) e v2
b) ve 2
c) 2 ve
d) e v 2
Answer: a

Question: Due to rotation of the earth the acceleration due to gravity g is
a) maximum at the equator and minimum at the poles
b) minimum at the equator and maximum at the poles
c) same at both places
d) None of the options
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: 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 kinetic energy of a satellite in its orbit around the earth is E. What should be the kinetic energy of the satellite so as to enable it to escape from the gravitational pull of the earth?
a) 4 E
b) 2 E
c) 2 E
d) E
Answer: b

Question: If value of acceleration due to gravity changes from one place to another, which of the following forces will undergo a change ?
a) Viscous force
b) Buoyant force
c) Magnetic force
d) All of the options
Answer: b

Question: The weight of an object in the coal mine, sea level and at the top of the mountain, are respectively W1, W2 and W3 then
a) W1< W2 > W3
b) W1= W2 = W3
c) W1< W2 < W3
d) W1> W2 > W3
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

Question: There are two bodies of masses 103 kg and 105 kg separated by a distance of 1 km. At what distance from the smaller body, the intensity of gravitational field will be zero
a) 1/9 km
b) 1/10 km
c) 1/11 km
d) 10/11 km
Answer: c

Question: The time period of an earth satellite in circular orbit is independent of
a) both the mass and radius of the orbit
b) radius of its orbit
c) the mass of the satellite
d) neither the mass of the satellite nor the radius of its orbit.
Answer: d

Question: There are _______ gravitational lines of force inside a spherically symmetric shell.
a) infinitely many
b) zero
c) varying number depending upon surface area
d) varying number depending upon volume
Answer: b

Question: Two 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: The amount of work done in lifting a mass ‘m’ from the surface of the earth to a height 2R is
a) 2mgR
b) 3mgR
c) 2/3 mgR
d) 3/2mgR
Answer: d

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

Question: A man waves his arms while walking. This is to
a) keep constant velocity
b) ease the tension
c) increase the velocity
d) balance the effect of earth’s gravity
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: d

Question: Mass of the Earth has been determined through
a) use of Kepler’s T2/R3 constancy law and Moon’s period
b) sampling the density of Earth’s crust and using Earth’s radius
c) Cavendish’s determination of G and using Earth radius and g at its surface
d) use of periods of satellites at different heights above Earth’s surface and known radius of Earth
Answer: c

Question: The escape velocity from the earth’s surface is 11 km/s. The escape velocity from a planet having twice the radius and same mean density as that of earth is
a) 5.5 km/s
b) 11 km/s
c) 22 km/s
d) None of the options
Answer: c

Question: The time period of a satellite in a circular orbit of radius R is T, the period of another satellite in a circular orbit of radius 4 R is
a) 4 T
b) T/4
c) 8 T
d) T/8
Answer: c

Question: The escape velocity of a body depends upon mass as
a) m0
b) m1
c) m2
d) m3.
Answer: a

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: 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 satellite is orbiting around the earth near its surface. If its kinetic energy is doubled, then
a) it will remain in the same orbit.
b) it will fall on the earth.
c) it will revolve with greater speed.
d) it will escape out of the gravitational field of the earth.
Answer: d

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: 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: If the mass of earth is eighty times the mass of a planet and diameter of the planet is one fourth that of earth, then acceleration due to gravity on the planet would be
a) 7.8 m/s²
b) 9.8 m/s²
c) 6.8 m/s²
d) 2.0 m/s²
Answer: d

Question: Time period of a simple pendulum inside a satellite orbiting earth is
a) zero
b) ¥
c) T
d) 2 T
Answer: b

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: Two point masses each equal to 1 kg attract one another with a force of 10^–10 N. The distance between the two point masses is (G = 6.6 × 10^–11 MKS units)
a) 8 cm
b) 0.8 cm
c) 80 cm
d) 0.08 cm
Answer: c

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 v₁and v₂ is
a) (r₁/r₂)²
b) r₂/r₁
c) ( r₂/r₁)²
d) r₁/ r₂
Answer: b

Question: Two bodies of masses 10 kg and 100 kg are separated by a distance of 2m ( G = 6.67 × 10^–11 Nm² kg^–2). The gravitational potential at the mid point on the line joining the two is
a) 7.3 × 10^–7 J/kg
b) 7.3 × 10^–9 J/kg
c) –7.3 × 10^–9 J/kg
d) 7.3 × 10^–6 J/kg
Answer: c

Question: The ratio of escape velocity at earth (ve) to the escape velocity at a planet (vp) 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: What would be the length of a sec. pendulum at a planet (where acc. due to gravity is g/4) if it’s length on earth is l
a) l/2
b) 2 l
c) l/4
d) 4 l
Answer: c

Question: If the length of a simple pendulum is increased by 2%, then the time period
a) increases by 2%
b) decreases by 2%
c) increases by 1%
d) decreases by 1%
Answer: c

Question: The radius of the earth is 4 times that of the moon and its mass is 80 times that of the moon. If the acceleration due to gravity on the surface of the earth is 10 m/s², then on the surface of the moon its value will be
a) 1 ms^–2
b) 2 ms^–2
c) 3 ms^–2
d) 4 ms^–2
Answer: b

Question: The distance of neptune and saturn from the sun is nearly 10¹³ and 10¹² meter respectively. Assuming that they move in circular orbits, their periodic times will be in the ratio
a) 10
b) 100
c) 1010
d) 1000
Answer: c

Question: A missile is launched with a velocity less than escape velocity. The sum of its kinetic and potential energies is
a) zero
b) negative
c) positive
d) may be positive, negative or zero.
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: 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: There is no atmosphere on the moon because
a) it is closer to the earth and also it has the inactive inert gases in it.
b) it is too for from the sun and has very low pressure in its outer surface.
c) escape velocity of gas molecules is greater than their root mean square velocity.
d) escape velocity of gas molecules is less than their root mean square velocity.
Answer: d

Question: If the change in the value of g at the height h above the surface of the earth is the same as at a depth ‘x’ below it, then (both x and h being much smaller than the radius of the earth)
a) x = h
b) x = 2 h
c) x = h/2
d) x = h2
Answer: b

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 mass of the moon is 1/81 of earth’s mass and its radius 1/4 that of the earth. If the escape velocity from the earth’s surface is 11.2 km/sec, its value from the surface of the moon will be
a) 0.14 kms^–1
b) 0.5 kms^–1
c) 2.5 kms^–1
d) 5.0 kms^–1
Answer: c

Question: Taking the gravitational potential at a point infinte distance away as zero, the gravitational potential at a point A is –5 unit. If the gravitational potential at point infinite distance away is taken as + 10 units, the potential at point A is
a) – 5 unit
b) + 5 unit
c) + 10 unit
d) + 15 unit
Answer: b

Question: A satellite of mass ‘m’, moving around the earth in a circular orbit of radius R, has angular momentum L. The areal velocity of satellite is (Me = mass of earth)
a) L /2m
b) L /m
c) 2L /m
d) 2L /Me
Answer: a

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: A planet of mass 3 × 10²⁹ gm moves around a star with a constant speed of 2 × 10⁶ ms^–1 in a circle of radii 1.5 × 10¹⁴ cm. The gravitational force exerted on the planet by the star is
a) 6.67 × 10²² dyne
d) 8 × 10²⁷ Newton
c) 8 × 10²⁶ N
d) 6.67 × 10¹⁹ dyne
Answer: c