Gravitational Force — Part 1 MCQs with Explanations

The Earth exerts a strong gravitational force that pulls objects toward its center. When an object is projected with a speed of about 7.9–8 km/s, it attains the first cosmic velocity (orbital velocity). At this speed, the object does not fall back to Earth because its forward motion continuously balances the pull of gravity. Instead of returning, the object keeps “falling around” the Earth, thereby moving in a circular or elliptical path. This speed is less than the escape velocity (11.2 km/s), so the object cannot leave Earth's gravitational field. Hence, the object will revolve around the Earth and enter into orbit.

On the moon, the gravitational acceleration ( g moon ) is 1/6 th that of the Earth. The height a person can jump is inversely proportional to the gravitational acceleration. So, if a person can jump 1.5 meters on Earth, then on the Moon, the jump height will be: Height on Moon = Height on Earth × (g earth / g moon ) = 1.5 × 6 = 9 meters Therefore, a person who jumps 1.5 m high on Earth can jump 9 m high on the Moon.

What is Gravitational Acceleration (g)? Imagine dropping a ball. It falls faster and faster! This increase in speed is due to gravitational acceleration . On the surface of the Earth, this acceleration is about 9.8 m/s² . This means for every second the ball falls, its speed increases by 9.8 meters per second. Does Gravity Change with Height? Yes! The force of gravity gets weaker the farther you are from the center of the Earth. So, if you go up into the sky, gravity won't pull you down quite as hard as it does on the ground. This means the gravitational acceleration will be less than 9.8 m/s² . The Formula We Use: To find the new gravitational acceleration (let's call it g' ) at a certain height ( h ) above the Earth's surface, we use this special formula: g' = g * (R / (R + h))² Let's understand what each part means: - g' : This is the new gravitational acceleration we want to find at height 'h'. - g : This is the gravitational acceleration on the Earth's surface , which is given as 9.8 m/s² . - R : This is the radius of the Earth (the distance from the Earth's center to its surface). We don't need its actual number because it will cancel out in our calculation. - h : This is the height above the Earth's surface . The question tells us this height is 1/10th of the Earth's radius . So, we can write h = R/10 . Now, Let's Calculate Step-by-Step! 1. First, substitute the value of 'h' into our formula: We know h = R/10 . So, our formula becomes: g' = 9.8 * (R / (R + R/10))² 2. Next, simplify the part inside the bracket (R + R/10): Imagine you have one whole pizza (R) and you add one-tenth of a pizza (R/10). Together, you have 11/10 of a pizza! So, R + R/10 = 10R/10 + R/10 = 11R/10 3. Put this simplified value back into the formula: g' = 9.8 * (R / (11R/10))² 4. Simplify the fraction (R divided by 11R/10): When you divide R by 11R/10, the 'R' on top and bottom cancels out. It becomes: R * (10 / 11R) = 10/11 5. Now, square this fraction: (10/11)² = (10 * 10) / (11 * 11) = 100 / 121 6. Finally, multiply this by 'g' (which is 9.8 m/s²): g' = 9.8 * (100 / 121) g' = 980 / 121 If you do this division, you get: g' ≈ 8.099 m/s² 7. Rounding this to one decimal place, we get approximately 8.1 m/s² . Does this Answer Make Sense? Yes! We expected the gravitational acceleration to be less than 9.8 m/s² because we are at a height above the Earth's surface. Our calculated value of 8.1 m/s² is indeed less than 9.8 m/s², which is a good sign! Comparing our result with the options: Option A: 4.0 m/s² Option B: 8.9 m/s² Option C: 4.5 m/s² Option D: 8.1 m/s² Our calculated value perfectly matches Option D . So, at 1/10th the height of Earth's radius, the gravitational acceleration will be approximately 8.1 m/s² !

Weightlessness is the condition in which a body experiences no net force of gravity acting on it. It does not mean that gravity disappears, but rather that both the body and its surroundings are in a state of free fall under the influence of gravity, creating the sensation of zero weight . Option B: Incorrect, because weightlessness is not due to decrease of gravity but due to free fall where gravitational pull is not felt. Option C: Incorrect, because even in a vacuum, gravity acts on bodies (for example, planets and satellites move in vacuum under gravity). Thus, weightlessness is correctly defined as zero gravity .

The weight of a human body is the force exerted on it due to gravity, and it depends on the gravitational acceleration at a given location. Option A: maximum at the poles – This is correct because the Earth is not a perfect sphere but an oblate spheroid, meaning it is slightly flattened at the poles and bulging at the equator. The distance from the center of the Earth to the poles is less than the distance to the equator. Since gravitational force is inversely proportional to the square of the distance from the center of the Earth, gravity is stronger at the poles, making the weight of a human body maximum at the poles. Option B: same at every place on the earth's surface – This is incorrect because the Earth's shape and rotation cause variations in gravitational force at different locations on its surface. Option C: maximum at the equator – This is incorrect because the equator is farther from the Earth's center compared to the poles, resulting in a slightly weaker gravitational force and thus lower weight at the equator. Option D: more on the mountains than planes – This is incorrect because altitude affects gravitational force, and as you go higher (such as on mountains), the distance from the Earth's center increases, resulting in a slightly lower gravitational force and less weight compared to sea level. Conclusion: The correct answer is Option A: maximum at the poles , as gravitational force is strongest at the poles, leading to a higher weight compared to other places on Earth.

Mass is constant and does not change with location Given mass = 600 kg Weight is calculated using W = m × g On the Moon, gravity is approximately 1/6th of Earth's gravity So, g (Moon) ≈ 9.8 / 6 ≈ 1.63 m/s² Now, Weight on Moon = 600 × 1.63 ≈ 978 N This is approximately equal to 960 N (nearest option) Hence, the correct answer is Option D .

Gravitational force is the correct answer to “The movement of the Moon around the Earth is due to . . . . . . . .”. This question is standard in competitive examination syllabi for Gravitational Force.

Satellite does not required any energy for orbiting is the correct answer to “Which one of the following statements about a satellite orbiting around the earth is correct”. This question is standard in competitive examination syllabi for Gravitational Force.

zero is the correct answer to “Astronauts feel . . . . . . . . weight inside the spacecraft.”. This question is standard in competitive examination syllabi for Gravitational Force.

moves with the same speed tangential to the original orbit is the correct answer to “A satellite revolves around the earth in a circular orbit. If gravitational pull suddenly disappear, then it”. This question is standard in competitive examination syllabi for Gravitational Force.

$$\frac{M}{{{R^2}}}$$ is the correct answer to “The acceleration due to gravity on the Earth's surface (mass M and radius R) is proportional to . . . . . . . .”. This question is standard in competitive examination syllabi for Gravitational Force.

6.6734 × 10-11 N - m2/kg2 is the correct answer to “What is the value of gravitational constant (G)”. This question is standard in competitive examination syllabi for Gravitational Force.

zero is the correct answer to “If the mass of the Sun, Earth and the distance between them are M, m and r respectively; The work done by the gravity of the Sun for a revolution around the Sun of the Earth.”. This question is standard in competitive examination syllabi for Gravitational Force.

Johannes Kepler is the correct answer to “Who proposed the laws of planetary motion”. This question is standard in competitive examination syllabi for Gravitational Force.

weightless is the correct answer to “Which condition does the body occur during free fall”. This question is standard in competitive examination syllabi for Gravitational Force.

decrease is the correct answer to “If satellite is shifted toward the earth. Then the time period of satellite will be”. This question is standard in competitive examination syllabi for Gravitational Force.

Laws of Planetary Motion is the correct answer to “Kepler discovered”. This question is standard in competitive examination syllabi for Gravitational Force.

Both 1 and 2 is the correct answer to “Consider the following statements. 1. According to Kepler's first law, each planet moves in an elliptical orbit around the sun, the sun being at one of the foci of the ellipse. 2. According to Kepler's Second Law, the radius vector of any planet relative to the sun sweeps out equal areas in equal times, that is the areal velocity of the radius vector of the planet is constant. Which of the statements given above is/are correct”. This question is standard in competitive examination syllabi for Gravitational Force.

98 N is the correct answer to “The mass of an object on Earth is 10kg. What is weight of object on Earth”. This question is standard in competitive examination syllabi for Gravitational Force.

increase in altitude from surface of the planet is the correct answer to “Acceleration due to gravity of planet decreases with . . . . . . . .”. This question is standard in competitive examination syllabi for Gravitational Force.

A planet's orbit is elliptical with the Sun at one of two focal points is the correct answer to “Which of the following statements is true about the motion of planets-”. This question is standard in competitive examination syllabi for Gravitational Force.

centre of gravity and centre of equilibrium fall within the feet is the correct answer to “It is easier to carry two buckets of water in one hand each than to carry only one in one hand because”. This question is standard in competitive examination syllabi for Gravitational Force.

the acceleration due to gravity in moon is smaller than that on the earth is the correct answer to “A person can jump higher on the moon's surface than on the earth because”. This question is standard in competitive examination syllabi for Gravitational Force.

increases is the correct answer to “When a body is moved from the equator to the north and south poles, its weight . . . . . . . .”. This question is standard in competitive examination syllabi for Gravitational Force.

3.2 m is the correct answer to “A truck slips off the edge and falls to the ground in 0.8 seconds. Which height will the edge be from the ground? (g = 10m/s 2 )”. This question is standard in competitive examination syllabi for Gravitational Force.

a-3, b-1, c-4, d-2 is the correct answer to “Match the following. List-I List-II a. Weight of a body is maximum 1. With increase in height from the surface of earth b. Weight of a body decreased 2. Null point c. Weight of a body increases 3. All the surface of earth d. Weight of the body is zero 4. When body is moved from null point towards moon”. This question is standard in competitive examination syllabi for Gravitational Force.

60 meters is the correct answer to “If a ball is thrown upwards with a velocity of 40 m/s, then what will be the magnitude of its displacement after 6 seconds? (g = 10 m/s 2 )”. This question is standard in competitive examination syllabi for Gravitational Force.

10 m/s2 is the correct answer to “The weight of an object on Earth is 200 N and mass is 20 kg. What will be the value of gravitational acceleration”. This question is standard in competitive examination syllabi for Gravitational Force.

9.8 meters per square second is the correct answer to “What is the value of acceleration due to gravity on the surface of the Earth”. This question is standard in competitive examination syllabi for Gravitational Force.

height is the correct answer to “The value of 'g' decreases according to-”. This question is standard in competitive examination syllabi for Gravitational Force.

(A) is true, but (R) is false is the correct answer to “Assertion (A): The weight of human being on the Moon is $$\frac{1}{6}$$ in comparison to Earth. Reason (R): The Moon does not have gravity like Earth. Select the answer.”. This question is standard in competitive examination syllabi for Gravitational Force.

$$\frac{1}{{36}}$$ times is the correct answer to “If the distance between two objects exceeds the normal distance by 6 times, the force of gravity will be-”. This question is standard in competitive examination syllabi for Gravitational Force.

Brahmagupta is the correct answer to “Who among the following anticipated Newton by declaring that all things gravitate to the Earth”. This question is standard in competitive examination syllabi for Gravitational Force.

Universal gravitational constant is the correct answer to “F = GM m/d 2 what is G called in the formula”. This question is standard in competitive examination syllabi for Gravitational Force.

$${R^{\frac{{\left( {n + 1} \right)}}{2}}}$$ is the correct answer to “Suppose the gravitational force changes inversely from the n power of the distance, then the time period of the planet revolving around the Sun in a circular orbit of R radius, will be proportional-”. This question is standard in competitive examination syllabi for Gravitational Force.

a-2, b-1, c-4, d-3 is the correct answer to “Which of the following pairs is correctly matched? List-I List-II a. Radium 1. Alexander Fleming b. Penicillin 2. Madam Curie c. X-ray 3. Edward Jenner d. Smallpox 4. W.K. Roentgen”. This question is standard in competitive examination syllabi for Gravitational Force.

Be shorter is the correct answer to “A girl is swinging on a swing in sitting position. When the girl stands up, the period of the swing will”. This question is standard in competitive examination syllabi for Gravitational Force.

Reach at the same time is the correct answer to “If pieces of equal size of woods, wax and iron falling from a same height, which one will reach the surface of the Earth first”. This question is standard in competitive examination syllabi for Gravitational Force.

Isaac Newton is the correct answer to “Who gave the theory of gravity”. This question is standard in competitive examination syllabi for Gravitational Force.

Just below the point of hanging is the correct answer to “Where is the center of gravity of an object hanging freely”. This question is standard in competitive examination syllabi for Gravitational Force.