Gravitation Practice Questions
20 free Gravitation practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
According to Newton's Universal Law of Gravitation, if the distance between two objects is tripled, how does the gravitational force between them change?
- A It becomes three times stronger.
- B It becomes one-third as strong.
- C It becomes nine times stronger.
- D It becomes one-ninth as strong.
Correct answer: It becomes one-ninth as strong.
Newton's law follows an inverse-square relationship where force is proportional to 1/r². If the distance r is tripled (3r), the force becomes proportional to 1/(3r)², which results in 1/9 of the original force.
What is the value of the acceleration due to gravity (g) at the exact center of the Earth?
- A 9.8 m/s²
- B 0 m/s²
- C 19.6 m/s²
- D 4.9 m/s²
Correct answer: 0 m/s²
At the center of the Earth, the mass of the Earth surrounds the object uniformly in all directions. The gravitational pulls from all sides cancel each other out, resulting in a net gravitational acceleration of zero.
Which of the following statements best describes the Universal Gravitational Constant (G)?
- A It varies depending on the altitude above sea level.
- B It is a scalar quantity with the same value everywhere.
- C It is a vector quantity pointing towards the center of a planet.
- D It depends on the medium between two interacting masses.
Correct answer: It is a scalar quantity with the same value everywhere.
The value G (approximately 6.674 x 10⁻¹¹ N·m²/kg²) is a fundamental physical constant. Unlike 'g', which changes with location, G is universal and does not change based on position or the surrounding environment.
If an astronaut travels from Earth to the Moon, how do their mass and weight change?
- A Both mass and weight decrease.
- B Mass decreases, but weight remains the same.
- C Mass remains the same, but weight decreases.
- D Both mass and weight remain the same.
Correct answer: Mass remains the same, but weight decreases.
Mass is an intrinsic property representing the amount of matter in an object and does not change with location. Weight is the force of gravity acting on that mass, and since the Moon's gravity is about 1/6th of Earth's, the astronaut's weight decreases.
What keeps a satellite in a stable circular orbit around the Earth?
- A The engine continuously firing to push it forward.
- B The complete absence of air resistance in the vacuum of space.
- C Centripetal force provided by Earth's gravitational pull.
- D The magnetic field of the Earth pushing it outward.
Correct answer: Centripetal force provided by Earth's gravitational pull.
A satellite is essentially in a state of perpetual free-fall. The Earth's gravity provides the necessary centripetal force to constantly change the satellite's direction, keeping it in a circular path rather than flying off in a straight line.
How does the acceleration due to gravity (g) change as one moves from the equator toward the poles of the Earth?
- A It remains constant.
- B It increases.
- C It decreases.
- D It first increases and then decreases.
Correct answer: It increases.
The Earth is an oblate spheroid, meaning it is slightly flattened at the poles and bulges at the equator. Because the polar radius is smaller than the equatorial radius, an object at the poles is closer to Earth's center and experiences a slightly higher value of g.
Which scientist is credited with the first accurate experimental measurement of the Universal Gravitational Constant (G)?
- A Isaac Newton
- B Galileo Galilei
- C Henry Cavendish
- D Johannes Kepler
Correct answer: Henry Cavendish
While Newton formulated the law of gravitation, he did not know the value of G. Henry Cavendish measured it in 1798 using a torsion balance, an experiment often referred to as 'weighing the Earth'.
Kepler's Second Law (the Law of Areas) implies that a planet moves fastest when it is at which point in its orbit?
- A Aphelion (its farthest point from the Sun)
- B Perihelion (its closest point to the Sun)
- C At either end of the orbit's minor axis
- D Its speed is constant throughout the orbit.
Correct answer: Perihelion (its closest point to the Sun)
Kepler's Second Law states that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. To sweep the same area when it is closer to the Sun (perihelion), the planet must travel a longer arc, meaning it moves faster.
What is the escape velocity from the surface of the Earth?
- A 9.8 km/s
- B 11.2 km/s
- C 42.1 km/s
- D 7.9 km/s
Correct answer: 11.2 km/s
Escape velocity is the minimum speed needed for a non-propelled object to break free from the gravitational influence of a celestial body. For Earth, this value is approximately 11.2 kilometers per second (or about 25,020 mph).
The variation of 'g' with height 'h' above the Earth's surface (where h is small compared to Earth's radius R) is approximately given by:
- A g' = g(1 - h/R)
- B g' = g(1 - 2h/R)
- C g' = g(1 + 2h/R)
- D g' = g(R²/h²)
Correct answer: g' = g(1 - 2h/R)
Using binomial expansion on the formula g' = GM/(R+h)², for small heights, the expression simplifies to g' = g(1 - 2h/R). This shows that gravity decreases linearly with small increases in altitude.
If the mass of the Earth were to double without changing its radius, what would happen to the weight of an object on its surface?
- A It would remain the same.
- B It would be halved.
- C It would be doubled.
- D It would quadruple.
Correct answer: It would be doubled.
Gravitational force is directly proportional to the product of the masses (F = G * m1 * m2 / r²). If one mass (the Earth) doubles while the other (the object) and the distance (radius) stay the same, the force (weight) doubles.
Tides in the Earth's oceans are primarily caused by:
- A The gravitational pull of the Sun acting alone.
- B The Earth's rotation and magnetic field.
- C The differential gravitational pull of the Moon and Sun.
- D Undersea earthquakes and volcanic activity on the ocean floor.
Correct answer: The differential gravitational pull of the Moon and Sun.
Tides are caused by the difference in gravitational pull exerted by the Moon (and to a lesser extent, the Sun) on different sides of the Earth. This differential force creates 'bulges' in the ocean water.
Which of the following is true regarding a geostationary satellite?
- A It orbits the Earth from North to South Pole.
- B Its orbital period is about 12 hours.
- C It appears fixed over one point on the equator.
- D It can be placed at any altitude above the Earth.
Correct answer: It appears fixed over one point on the equator.
A geostationary satellite has an orbital period of 24 hours, matching the Earth's rotation. By orbiting directly above the equator in the same direction as Earth's rotation, it stays fixed over the same geographic longitudinal point.
What happens to the gravitational potential energy of an object as it is moved farther away from the Earth?
- A It increases (becomes less negative).
- B It decreases (becomes more negative).
- C It remains constant.
- D It becomes zero at the surface.
Correct answer: It increases (becomes less negative).
Gravitational potential energy is defined as U = -GMm/r. As the distance 'r' increases, the fraction becomes a smaller negative number, which mathematically represents an increase in energy.
Two spheres of lead are resting on a table with a certain distance between them. If the air between them is replaced with water, the gravitational force between them will:
- A Increase slightly
- B Decrease slightly
- C Become zero
- D Remain the same
Correct answer: Remain the same
The gravitational force between two masses is independent of the intervening medium. Unlike electrostatic force, which changes with the dielectric constant of the medium, gravity depends only on masses and distance.
The time period of a simple pendulum inside a satellite orbiting the Earth is:
- A The same as on Earth
- B Zero
- C 2 seconds
- D Infinite
Correct answer: Infinite
In an orbiting satellite, objects are in a state of weightlessness (effective g = 0). Since the period of a pendulum is T = 2π√(L/g), if g is zero, the period becomes infinite, meaning the pendulum will not oscillate.
If the Earth suddenly stops rotating, the value of 'g' at the equator will:
- A Increase
- B Decrease
- C Remain unchanged
- D Become zero
Correct answer: Increase
The Earth's rotation creates a centrifugal effect that slightly reduces the effective gravitational pull at the equator. If rotation stops, this outward 'force' disappears, and the measured acceleration due to gravity would increase slightly.
Which law states that the square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit?
- A Kepler's First Law
- B Kepler's Second Law
- C Newton's Third Law
- D Kepler's Third Law
Correct answer: Kepler's Third Law
Kepler's Third Law, also known as the Law of Harmonies, provides the mathematical relationship (T² ∝ r³) between a planet's distance from the Sun and its orbital period.
Weightlessness experienced in a spaceship is due to:
- A Gravity being too weak to act at orbital heights.
- B The spaceship being located at a point of zero gravity.
- C The vacuum of space surrounding the spaceship.
- D The spaceship and its occupants being in free-fall.
Correct answer: The spaceship and its occupants being in free-fall.
Astronauts feel weightless not because gravity is absent (Earth's gravity at the ISS is still about 90% of surface gravity), but because they are in continuous free-fall. Without a normal force from a floor pushing back, they experience the sensation of weightlessness.
What is the gravitational field strength at a point where a 2 kg mass experiences a gravitational force of 20 N?
- A 10 N/kg
- B 40 N/kg
- C 5 N/kg
- D 20 N/kg
Correct answer: 10 N/kg
Gravitational field strength (E) is defined as the force (F) per unit mass (m). Calculating E = F/m = 20 N / 2 kg gives a field strength of 10 N/kg.