NEET Physics Gravitation MCQs Set A

a) cannot be zero at any point

b) will be same everywhere in magnitude directed towards the centre

c) will have the same value everywhere but not directed towards the centre

d) will be directed towards the centre but not the same everywhere

Answer: cannot be zero at any point

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) not be true because the major gravitational force on mercury is due to the sun

b) not be true because mercury is influenced by forces other than gravitational force

c) not be true because the force between the earth and mercury is not inverse square law

d) be similarly true

Answer: not be true because the major gravitational force on mercury is due to the sun

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: the torque is zero

Question: Satellites orbitting the earth have finite life and sometimes debris of satellites fall to the earth. This is because

a) of viscous forces causing the speed of satellite and hence height to gradually decrease

b) of collisions with other satellites

c) the laws of gravitation predict a trajectory spiralling inwards

d) the solar cells and batteries in satellites run out

Answer:  of viscous forces causing the speed of satellite and hence height to gradually decrease

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 not be strictly elliptical because the total gravitational force on it is not central

b) is not elliptical but will necessarily be a closed curve

c) deviates considerably from being elliptical due to influence of planets other than the earth

d) None of these

Answer:  will not be strictly elliptical because the total gravitational force on it is not central

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 move in orbits like planets and obey Kepler's laws

b) will move around the sun in closed orbits but not obey Kepler's laws

c) will move in an irregular way because of their small masses and will drift away into outer space

d) will not move around the sun, since they have very small masses compared to the sun

Answer: will move in orbits like planets and obey Kepler's laws

Question: Choose the wrong option

a) Gravitational mass of a particle like proton can depend on the presence of neighbouring heavy objects but the inertial mass cannot

b) 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

c) That the gravitational mass and inertial mass are equal is an experimental result

d) 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

Answer: Gravitational mass of a particle like proton can depend on the presence of neighbouring heavy objects but the inertial mass cannot

Question:

a) m will move towards 2M

b) m will have oscillatory motion

c) m will move towards M

d) m will remain at rest

Answer: m will move towards 2M

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^{– 2} m

b) 100 m

c) 10^{– 6} m

d) 10^{– 9} m

Answer:  10^{– 2} m

Question:  The potential energy of a satellite of mass m and revolving at a height R_e above the surface of earth where R_e = radius of earth, is

a)

b)

c)

d)

Answer:

Question:  Four particles, each of mass M and equidistant from each other, move along a circle of radius R under the action of their mutual gravitational attraction. The speed of each particle is:

a)

b)

c)

d)

Answer:

Question:

a)

b)

c) Both

d) None of these

Answer:

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 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 linear momentum of S remains constant in magnitude.

d) the total mechanical energy of S varies periodically with time

Answer: the acceleration of S is always directed towards the centre of the earth

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) 7.76 km s^-1

b) 9.13 km s^-1

c) 8.56 km s^-1

d) 6.67 km s^-1

Answer:  7.76 km s^-1

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) + 10 unit

c) + 15 unit

d) – 5 unit

Answer:  + 5 unit

More Questions..........................................................

Question:

a)

b)

c)

d)

Answer:

Question:  An artificial satellite is moving in a circular orbit around the earth with a speed equal to half the magnitude of the escape velocity from the earth. The height (h) of the satellite above the earth’s surface is (Take radius of earth as R_e)

a)

b)

c)

d)

Answer:

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)

b) 1 : 4

c) 1 : 2

d) 1 : 3

Answer: 

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:  2600 km

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)

b) 1000

c) 100

d) 10

Answer:

Question:  A satellite is revolving in a circular orbit at a height 'h' from the earth's surface (radius of earth R; h < < R). The minimum increase in its orbital velocity required, so that the satellite could escape from the earth's gravitational field, is close to :

(Neglect the effect of atmosphere.)

a)

b)

c)

d)

Answer:

Question:

a) 7.8 × 10^–4 rad/s

b) 7.4 × 10^–3 rad/s

c) 8.7 × 10^–7 rad/s

d) 6.7 × 10^–4 rad/s

Answer:  7.8 × 10^–4 rad/s

Question:

a)

b)

c)

d)

Answer:

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 = 2 km

b) d = 1 km

c)

d) None of these

Answer: d = 2 km

Question: The change in the value of ‘g’ at a height ‘h’ above the surface of the earth is the same as at a depth ‘d’ below the surface of earth. When both ‘d’ and ‘h’ are much smaller than the radius of earth, then which one of the following is correct?

a) d =2 h

b) d = h

c)

d) None of these

Answer:  d =2 h

Question: Assertion : Space rocket are usually launched in the equatorial line from west to east
Reason : The acceleration due to gravity is minimum at the equator

a) Assertion is correct, reason is correct; reason is not a correct explanation for assertion

b) Assertion is correct, reason is incorrect

c) Assertion is incorrect, reason is correct

d) Assertion is correct, reason is correct; reason is a correct explanation for assertion

Answer: Assertion is correct, reason is correct; reason is not a correct explanation for assertion

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: move towards each other

Question:  What is the minimum energy required to launch a satellite of mass m from the surface of a planet of mass M and radius R in a circular orbit at an altitude of 2R?

a)

b)

c)

d) None of these

Answer:

Question: A body moves in a circular orbit of radius R under the action of a central force. Potential due to the central force is given by V(r) = kr (k is a positive constant). Period of revolution of the body is proportional to

a) R^1/2

b) R^–1/2

c) R^–3/2

d) R^–5/2

Answer:  R^1/2

Question:  The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are K_A, K_B and K_C, respectively. AC is the major axis and SB is perpendicular to AC at the position of the Sun S as shown in the figure. Then

a)

b)

c)

d) None of these

Answer:

Question: If the mass of the Sun were ten times smaller and the universal gravitational constant were ten times larger in magnitude, which of the following is not correct?

a) ‘g’ on the Earth will not change

b) Time period of a simple pendulum on the Earth would decrease

c) Walking on the ground would become more difficult

d) Raindrops will fall faster

Answer:  ‘g’ on the Earth will not change

Question:

a) 1 J

b) 71 J

c) –71 J

d) None of these

Answer:  1 J

Question:

a) 2G

b) 4G

c) G/2

d) G

Answer:  2G

Question:

a)

b)

c)

d) None of these

Answer:

Question: The true weight of an object in a geostationary satellite that weighed exactly 10.0N at the north pole

a) 0.23 N

b) 2.33 N

c) 10.0 N

d) 12.1 N

Answer: 0.23 N

Question:   Two spherical bodies of mass M and 5M & radii R & 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) 4.5 R

b) 7.5 R

c) 1.5 R

d) 2.5 R

Answer: 4.5 R

Question:  The percentage change in the acceleration of the earth towards the sun from a total eclipse of the sun to the point where the moon is on a side of earth directly opposite to the sun is

a)

b)

c)

d)

Answer:

Question:  If the Earth has no rotational motion, the weight of a person on the equator is W. Determine the speed with which the earth would have to rotate about its axis so that the person at the equator will weight 3/4W. Radius of the Earth is 6400 km and g =10 m/s².

a)

b)

c)

d)

Answer:

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 increases by 4% and K decreases by 4%

b) g decreases by 4% and K increases by 4%

c) g decreases by 4% and K increases by 2%

d) g decreases by 2% and K decreases by 4%

Answer:  g increases by 4% and K decreases by 4%

Question:

a)

b)

c)

d) None of these

Answer:

Question:

a)

b)

c)

d)

Answer:

Question:

a) K/2x²

b) K/x²

c) K/2x

d) K/x

Answer:  K/2x²

Question:

a)

b)

c)

d)

Answer:

Question:  Imagine a light planet revolving around a very massive star in a circular orbit of radius R with a period of revolution T. Ifthe gravitational force of attraction between the planet and the star proportional to R^–5/2, then :

a)

b)

c)

d) None of these

Answer:

Question:  For a satellite orbiting in an orbit, close to the surface of earth, to escape, what is the percentage increase in the kinetic energy required?

a) 41%

b) 61%

c) 81%

d) 98%

Answer:  41%

Question:

a)

b)

c) zero

d) None of these

Answer:

Question:  A satellite of mass m is orbiting the earth in a circular orbit ofradius R. It starts losing energy due to small air resistance at the rate of C J/s. Find the time taken for the satellite to reach the earth.

a)

b)

c)

d) None of these

Answer:

Question:  If suddenly the gravitational force of attraction between earth and a satellite revolving around it becomes zero, then the satellite will

a) move tangentialy to the original orbit in the same velocity

b) become stationary in its orbit

c) Both

d) None of these

Answer:  move tangentialy to the original orbit in the same velocity

Question:  When does the object in a satellite escapes to infinity?

a) Both

b) When the total energy is positive

c) When total energy is zero

d) All of these

Answer: Both

Question:  An artificial satellite orbiting the earth does not fall down because the earth’s attraction

a) None of these

b) is balanced by the viscous drag produced by the atmosphere

c) vanishes at such distances

d) is balanced by the attraction of the moon

Answer:  None of these