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Foundation1 past question

Gravitational field and potential

The gravitational field describes the force per unit mass at a point in space due to one or more masses, while gravitational potential is the work done per unit mass to bring a mass from infinity to that point.

Why this shows up in the exam

You need to calculate field intensity, potential, and understand their relationship for NEET problems.

How NEET tests this

Numerical · 3 Qs

Learn the idea

Gravitational field intensity is the force that a unit mass would feel at a point, while gravitational potential is the work needed per unit mass to bring it from infinity. The key insight: field = force / mass and potential = work / mass, so once you know one you can get the other by differentiation or integration.

🧠 Memory hook: Think of g as ‘weight per kilogram’ – just how heavy you feel per each kilogram of your own mass.

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

Formulas & facts to keep ready

  • g = F / m (unit N kg⁻¹)
  • Gravitational potential V = –GM / r (unit J kg⁻¹)
  • Relation: g = –dV/dr (magnitude g = |dV/dr|)
  • Superposition holds for both field and potential
  • SI units: mass in kg, distance in m, force in N
  • Potential is scalar, field is vector

How to approach it

  1. 1Read the question and list what is given – force, mass, distance, etc.
  2. 2Convert every quantity to SI units (g → kg, cm → m).
  3. 3Apply the definition that matches the asked quantity – use g = F/m for field, V = –GM/r for potential.
  4. 4If both field and potential appear, use g = –dV/dr or integrate accordingly.

Worked example — watch it click

A body of mass 60 g experiences a gravitational force of 3.0 N, when placed at a particular point. The magnitude of the gravitational field intensity at that point is:

  • A)0.05 N/kg
  • ✅50 N/kg
  • C)20 N/kg
  • D)180 N/kg

The concept behind this problem

The example checks whether you can translate the definition of gravitational field intensity into a numerical answer by correctly handling the force‑per‑unit‑mass relation.

Step by step

  1. 1The gravitational field intensity (often denoted g) at a point is defined as the force per unit mass placed at that point: g = (F)/(m).
  2. 2The mass of the body is 60 g, which is 60/1000 = 0.06 kg.
  3. 3The gravitational force acting on it is 3.0 N.
  4. 4Now compute the field intensity: g = 3.0 N0.06 kg = 50 N kg⁻¹.
  5. 5Thus the field intensity is 50 N per kilogram.
  6. 6The option “0.05 N/kg” would correspond to using the mass in grams directly, which is incorrect because the SI unit of mass is kilogram.
  7. 7So the correct answer is 50 N/kg.

Watch out

Students often forget to change 60 g to 0.06 kg, leading to the wrong 0.05 N kg⁻¹ option.

Common slip-ups that cost marks

  • •Using gram directly instead of kilogram gives a factor 1000 error
  • •Ignoring the negative sign of potential – it is always negative for attractive gravity
  • •Treating potential as a vector; it is a scalar quantity

🌟 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 1NEET 2022

A body of mass 60 g experiences a gravitational force of 3.0 N, when placed at a particular point. The magnitude of the gravitational field intensity at that point is:

Push further

More challenging

2 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 2

A spherical planet has a mass of 5.0 x 10²³ kg and a radius of 2.0 x 10⁶ m. What is the gravitational field intensity on its surface? (Given G = 6.67 x 10⁻¹¹ N m²/kg²)

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