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Question

The force exerted by the earth on the moon is: 
(Consider G=\(6 \times 10^{-11}Nm^2kg^{-2}\) ; mass of the earth M=\(6 \times 10^{24}\)kg; mass of the moon= \(8 \times 10^{22}\) kg, and distance between earth and moon is \(4 \times 10^{8}\) m).

This question was previously asked in
RRB NTPC 2024 Undergraduate CBT 1 Question Paper (29-Aug-2025) (Shift 1)
The correct answer is

 $1.8 \times 10^{20}$ N

Understanding Gravitational Force Calculation

The question asks us to calculate the force exerted by the Earth on the Moon using the provided values for the gravitational constant (\(G\)), the mass of the Earth (\(M\)), the mass of the Moon (\(m\)), and the distance between them (\(r\)). This force is governed by Newton's Law of Universal Gravitation.

Newton's Law of Universal Gravitation

Newton's Law of Universal Gravitation states that every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. The formula is:

\( F = G \frac{Mm}{r^2} \)

Where:

  • \(F\) is the gravitational force between the two bodies.
  • \(G\) is the universal gravitational constant.
  • \(M\) is the mass of the larger body (Earth).
  • \(m\) is the mass of the smaller body (Moon).
  • \(r\) is the distance between the centers of the two bodies.

Given Values

Let's list the values provided in the question:

Gravitational Constant (\(G\)) \(6 \times 10^{-11} \, \text{Nm}^2\text{kg}^{-2}\)
Mass of Earth (\(M\)) \(6 \times 10^{24} \, \text{kg}\)
Mass of Moon (\(m\)) \(8 \times 10^{22} \, \text{kg}\)
Distance (\(r\)) \(4 \times 10^{8} \, \text{m}\)

Step-by-Step Force Calculation

Now, we will substitute these values into the gravitational force formula:

  1. Calculate the product of the masses (\(Mm\)): \( Mm = (6 \times 10^{24} \, \text{kg}) \times (8 \times 10^{22} \, \text{kg}) \) \( Mm = (6 \times 8) \times 10^{(24+22)} \, \text{kg}^2 \) \( Mm = 48 \times 10^{46} \, \text{kg}^2 \)
  2. Calculate the square of the distance (\(r^2\)): \( r^2 = (4 \times 10^{8} \, \text{m})^2 \) \( r^2 = 4^2 \times (10^{8})^2 \, \text{m}^2 \) \( r^2 = 16 \times 10^{16} \, \text{m}^2 \)
  3. Substitute \(Mm\) and \(r^2\) into the formula part \(\frac{Mm}{r^2}\): \( \frac{Mm}{r^2} = \frac{48 \times 10^{46} \, \text{kg}^2}{16 \times 10^{16} \, \text{m}^2} \) \( \frac{Mm}{r^2} = \left(\frac{48}{16}\right) \times 10^{(46-16)} \, \frac{\text{kg}^2}{\text{m}^2} \) \( \frac{Mm}{r^2} = 3 \times 10^{30} \, \frac{\text{kg}^2}{\text{m}^2} \)
  4. Multiply by the gravitational constant (\(G\)) to find the force (\(F\)): \( F = G \times \frac{Mm}{r^2} \) \( F = (6 \times 10^{-11} \, \text{Nm}^2\text{kg}^{-2}) \times (3 \times 10^{30} \, \frac{\text{kg}^2}{\text{m}^2}) \) \( F = (6 \times 3) \times 10^{(-11+30)} \, \text{N} \) \( F = 18 \times 10^{19} \, \text{N} \)
  5. Express the final answer in standard scientific notation: \( F = 1.8 \times 10^1 \times 10^{19} \, \text{N} \) \( F = 1.8 \times 10^{20} \, \text{N} \)

Conclusion

The calculated force exerted by the Earth on the Moon is \(1.8 \times 10^{20}\) N. This matches one of the options provided.

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Similar Questions

  1. The gravitational force between two objects of masses m1 and m2 is directly proportional to

  2. Which of the following statements is/are correct?

    Statements:

    I) The mass of an object is the same as its weight.

    II) The mass of an object is not the same as its weight.

    III) Mass is scalar quantity, whereas weight is vector quantity.

  3. Which of the following statements is/are correct?

    Statements:

    I) The Gravitational force between two objects is independent of the distance of separation between two objects.

    II) The Gravitational force between two objects is inversely proportional to the square of the distance of the separation between two objects.

    III) The Gravitational force between two objects is directly proportional to the product of their masses.

  4. When an object falls under gravity, the object experiences:

  5. If the acceleration due to gravity of the earth is 6 times the acceleration due to gravity on the moon, which of the following statements is correct?

  6. Energy possessed by a body by virtue of its position or configuration is:

  7. Which of the following statements is/are INCORRECT?

    A. The value of G on the moon is equal to that on the earth.
    B. $26.68 \times 10^{-11}$ N is the force of gravitation between two point masses of 2 kg and 2 kg kept 1 m apart.
    C. Newton's law of gravitation is valid in the laboratory only.
    D. Force is inversely proportional to the square of the distance between two bodies.
  8. What will be the force of attraction between two bodies weighing 20 kg and 50 kg, respectively, with a distance of 2 metre between them?

Important Questions from Gravitation

  1. The known forces of nature can be divided into four classes, viz., gravity, electromagnetism, weak nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?

  2. A spacecraft of mass m = 1000 kg has a fully reflecting sail that is oriented perpendicular to the direction of the sun. The sun radiates 10 26 W and has a mass M = 10 30  kg. Ignoring the effect of the planets, for the gravitational pull of the sun to balance the radiation pressure on the sail, the area of the sail will be
  3. The force of attraction between two bodies separated by a distance of d is F. The distance for which the force of attraction between them is 64 F is ________.

  4. If two satellites of masses m1 and m2 are revolving around a earth in a circular orbits of radius r1 and r2, then the ratio of their orbital velocities \(\dfrac{v_1}{v_2}\) is

  5. A women whose mass is 60 kg on the earth surface is in an spacecraft at an altitude of two times the earth radius. Her mass there is

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