Physics

Gravitation and Orbital Mechanics

500 Questions

Gravitation and orbital mechanics focus on planetary motion, elliptical orbits, and satellite deployment. Questions examine astrodynamics fundamentals, including geostationary orbits and perturbation theory. These topics are highly relevant for civil services and specialized technical examinations.

Planetary orbitsSatellite dynamicsGeostationary orbitsPerturbation theoryOrbital eccentricity

Gravitation and Orbital Mechanics Questions

Multiple choice

The word “orbit” could most nearly mean

Directions: Read the passage carefully and answer the question that follows.


There are millions of stars in the sky. We see many of them in the night sky. But, we can see only one during the day – the sun. The sun is also a star like so many others in the sky. But, it is ‘our’ star. It is the head of and at the centre of the family we call “The solar system”. All the planets in the solar system revolve around the sun.  Till recently, we were told that there are nine planets in the solar system, Mercury being the nearest to the sun and Pluto the most distant; Jupiter being the largest and Pluto again being the smallest. Some astronomers believe there could be more. They say that Pluto is too small to be called a planet.  It is a dwarf planet, though still much bigger than ordinary asteroids. The planets move around the sun in a definite orbit. This is what prevents them from striking each other.

  1. a shape

  2. a square

  3. a method

  4. a path
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In the context of the passage, 'orbit' refers to the definite path that planets follow around the sun.

Multiple choice

What does ‘it orbits Earth’ mean in the passage?

Directions: The passage is followed by five questions. Read the passage carefully and answer the question that follows. For the question four probable answers bearing options (1), (2), (3) and (4) are given. Only one out of those is correct. You have to choose correct answer.

The Hubble enables us to see farther than any telescope on Earth. It has helped us learn about how solar systems and galaxies form, as well as the existence of dark energy, a mysterious force that causes the universe to expand. Hubble, the powerful telescope, is the size of a school bus. It orbits Earth every 97 minutes, moving five miles per second. Since Hubble is beyond Earth’s atmosphere, it can take clearer pictures of outer space than any telescope on Earth.

  1. Hubble telescope revolves around Earth.

  2. Dark energy revolves around Earth.

  3. Dark energy makes Earth revolve around it.

  4. Hubble telescope has more speed than a school bus.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Here, ‘it’ refers to ‘the Hubble telescope’ and ‘orbit’ means ‘to revolve around something’.

Multiple choice

Each planet tends to the roughly twice as far from the sun as its next Sunward neighbour. This is called

  1. Hawkins's Law

  2. Bode's Law

  3. Bagnold's Law

  4. All of the above

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Bode law is a hypothesis that the bodies in some orbital systems, including the Sun's, orbit at semi-major axes in a function of planetary sequence. The hypothesis correctly predicted the orbits of Ceres and Uranus, but failed as a predictor of Neptune's orbit. According to this law each planet tends to the roughly twice as far from the sun as its next Sunward neighbor.

Multiple choice

A superior planet is the one whose

  1. orbit lies within that of the earth

  2. orbit lies beyond that of the earth

  3. speed of rotation round its axis is less that that of the earth

  4. speed round the sun is more that of the earth

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A planet which orbits the Sun outside of the Earth's orbit. The superior planets are Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and most of the minor planets. Mercury and Venus, on the other hand, are inferior planets because they orbit the Sun inside the Earth's orbit. Superior planets orbit the Sun more slowly than the Earth, and experience oppositions and superior conjunctions.

Multiple choice

Satellites used for telecommunications relay are kept in a geostationary orbit. A satellite is said to be in such an orbit when

  1. The orbit is geosynchronous.
  2. the orbit is circular.
  3. The orbit lies in the place of the Earth’s equator.
  4. The orbit is at an altitude of 22,236 km.

Select the correct answer using the codes given below:

  1. 1, 2 and 3 only

  2. 1, 3 and 4 only

  3. 2 and 4 only

  4. All 1, 2, 3 and 4
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Statement 1 is correct. A geostationary orbit (or Geostationary Earth Orbit - GEO) is a type of geosynchronous orbit directly above the Earth\'s equator (0° latitude).

Statements 2 and 3 are correct. A satellite in a synchronous orbit that is both equatorial and circular will appear to be suspended motionless above a point on the orbited planet\'s equator. Statement 4 is incorrect. Geostationary orbit is at an altitude of 22, 236 miles, not km. In km, the altitude comes to be 35,786 km.
Multiple choice

An artificial satellite orbiting around the Earth does not fall down. This is so because the attraction of Earth.

  1. does not exist at such distance.

  2. is neutralized by the attraction of the moon.

  3. provides the necessary speed for its steady motion.

  4. provides the necessary acceleration for its motion.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

An artificial satellite moving round the Earth in a circular orbit possesses an acceleration, which is constant in magnitude but changing in direction,. The artificial satellite revolves round the Earth under centripetal acceleration. The launched satellite should have the speed enough so that gravity doesn't bring the satellite back to the Earth, but no so great that it escapes in the space. It means the speed provided by the rocket is the source of centrifugal force, and the Earth's attraction holds it from  moving away from this centrifugal force.

Multiple choice

Assertion A: The same face of moon is always presented to Earth. Reason R: The moon rotates about its own axis in 23 and a half days, which is about the same time that it takes to orbit Earth.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is NOT the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

We see the same face of moon from Earth because the moon rotates about its own axis in 23 and a half days, which is about the same time that it takes to orbit Earth. 

Multiple choice

Assertion A: To orbit around Sun, the planet Mars takes lesser time than Earth. Reason R: The diameter of the planet Mars is less than that of Earth.

  1. Both ‘A’ and ‘R’ are true and ‘R’ is the correct explanation of ‘A’.

  2. Both ‘A’ and ‘R’ are individually true, but ‘R’ is not the correct explanation of ‘A’.

  3. ‘A’ is true, but ‘R’ is false.

  4. ‘A’ is false, but ‘R’ is true.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A is incorrect as Mars' revolution around the Sun takes 1.88 years of Earth’s revolution. The diameter of Earth is 12,742 km (7,918 miles) and the mass is 6,734 km (4,200 miles).

Multiple choice physics universe and space science launching of an artificial satellites around the earth launching of satellite india’s space programmes

Communication satellites move in orbits of radius 44,400 km around the earth find the acceleration of such a satelite, assuming that the only force acting on, it is that  due to the earth.Mass of the earth $ = 6 \times {10^{24}}Kg.$

  1. $0.2\;m{s^{ - 2}}$
  2. $2.1\;m{s^{ - 2}}$
  3. $4.2\;m{s^{ - 2}}$
  4. $0.3\;m{s^{ - 2}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The acceleration (a) of a satellite in orbit is given by the gravitational field strength: a = GM / r^2. Using G = 6.67e-11, M = 6e24, and r = 4.44e7 meters, a = (6.67e-11 * 6e24) / (4.44e7)^2 = 4e14 / 1.97e15 = 0.203 m/s^2.

Multiple choice physics universe and space science launching of an artificial satellites around the earth launching of satellite india’s space programmes

In case of an orbiting satellite, if the radius of orbit is decreased.

  1. Its KE decreases

  2. Its PE decreases

  3. Its ME decreases

  4. Its speed decreases
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

P.E of orbiting satellite at distance $r$ from centre of earth

$=\cfrac{-GMm}{r}\\K.E=\cfrac{GMm}{2R}$ and $M.E=\cfrac{-GMm}{2R}$

If $R$ decreased K.E increases.

P.E and M.E become more negative, thus decrease.

Multiple choice physics universe and space science launching of an artificial satellites around the earth launching of satellite india’s space programmes

Two identical satellites are moving in the same circular orbit around the earth but in opposite senses of rotation, Assuming an inelastic collision to take place, so that the wreckage remains as one piece of tangled material  wreckage

  1. will be moving in a circular orbit of half the radius

  2. will be moving in a circular orbit on one fourth the radius

  3. will spin with no translatory motion

  4. falls directly down
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The wreckage will spin with no translatory motion$.$

Hence,
option $(C)$ is correct answer.