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Exam level3 past questions

Newton's law of universal gravitation

Newton's law of universal gravitation states that every two masses attract each other with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Why this shows up in the exam

NEET tests your understanding of the law, its mathematical form, and its implications for planetary and satellite motion.

How NEET tests this

Statement analysis · 2 QsApplication

Learn the idea

Newton’s law of universal gravitation says that any two masses attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. The key insight is that changing both masses and distance together can leave the force unchanged because the changes cancel in the ratio.

🧠 Memory hook: Gravity is a twin‑balance: double both twins and also double the rope (distance) – the pull stays the same, just like a seesaw that stays level when both sides are equally weighted.

Get this one clearly and it pays off every single time it shows up in the paper. 🎯

Formulas & facts to keep ready

  • F = G·m₁·m₂ / r² (NCERT Eq. 8.1)
  • G = 6.67×10⁻¹¹ N·m²·kg⁻² – universal constant
  • Force acts along the line joining the centres of the two masses
  • Inverse‑square dependence: if r is doubled, force becomes one‑fourth
  • Direct proportionality: if either mass is doubled, force doubles

How to approach it

  1. 1Identify the two masses (m₁,m₂) and their separation r
  2. 2Write the expression F = G·m₁·m₂ / r²
  3. 3Apply the given change (double, halve, etc.) to numerator and denominator separately
  4. 4Compare the new expression with the original to see how F changes

Worked example — watch it click

Assertion (A): When distance between bodies is doubled and mass of each body is also doubled, gravitational force between them remains the same. Reason (R): According to Newton's law gravitational, force is directly proportional to mass of bodies and inversely proportional to square of distance between them.

  • ✅If both assertion and reason are true, and reason is the correct explanation of assertion.
  • B)If both assertion and reason are true, but reason is not the correct explanations of assertion.
  • C)If assertion is true, but reason is false.
  • D)If both assertion and reason are false.

The concept behind this problem

The worked example asks you to see how simultaneous doubling of both masses and the separation influences the numerator and denominator of the law, testing the proportional reasoning behind the inverse‑square formula.

Step by step

  1. 1Newton's law: F = Gm₁m₂/r².
  2. 2Initially F = Gm₁m₂/r².
  3. 3After changes: F' = G(2m₁)(2m₂)/(2r)² = 4Gm₁m₂/4r² = Gm₁m₂/r² = F.
  4. 4The force remains the same.
  5. 5Reason correctly states F ∝ m₁m₂ and F ∝ 1/r², which explains why doubling both masses and distance keeps F constant.
  6. 6Both A and R are true, and R correctly explains A.

Watch out

Students often double the force because the masses double, overlooking that the distance also doubles and its square reduces the force by a factor of four.

Common slip-ups that cost marks

  • •Treating “power” as the same as “force” – they are different physical quantities
  • •Forgetting that the distance appears as r², not r
  • •Assuming G changes with the medium; G is a universal constant

🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.

Practise it

These are real questions from past NEET papers that test this exact idea.

Question 1 of 3

A body projected vertically from the Earth reaches a height equal to the radius of the Earth before returning to Earth. The power exerted by gravitational force is greatest (a) at the highest position of the body. (b) at the instant just before the body hits the earth. (c) it remains constant all through. (d) at the instant just after the body is projected.

Push further

More challenging

9 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.

Question 1 of 9

A rocket is launched vertically upwards from the Earth's surface with an initial velocity. Assuming only gravitational force acts on it, at what point during its upward journey is the power exerted by gravity at its maximum magnitude?

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