NEET Physics Gravitation MCQs Set A

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: A

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) 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: 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 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: A

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: A

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: A

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: A

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: 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) 7.76 km s^-1
(b) 9.13 km s^-1
(c) 8.56 km s^-1
(d) 6.67 km s^-1

Answer: A

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: 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. 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: A

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 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: A

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: A

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: A

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: A

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: A

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: A

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: A

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: A

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: A