Gravitation Exemplar — Class 9 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 9 Science chapter "Gravitation Exemplar" — 5 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 9 Science chapter "Gravitation Exemplar" — 5 important questions with detailed answers for CBSE board exam…
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NCERT Solutions for Class 9 Science — Gravitation Exemplar. Step-by-step answers to all 5 textbook questions from this chapter, written for CBSE board preparation and free to use.
Gravitation Exemplar — All 5 Questions Solved
Q1. Calculate the gravitational force between two masses 5 kg and 10 kg separated by 2 m. (G = 6.67 × 10^-11 N·m²/kg²)
F = G(m1 × m2)/r² = (6.67 × 10^-11)(5)(10)/(4) = (6.67 × 10^-11)(50/4) = 8.34 × 10^-10 N.
Q2. Why is the weight of an object less on the moon than on Earth?
Weight is W = mg, where g depends on mass and radius of celestial body: g = GM/R². Moon has smaller mass and radius than Earth, so g_moon = 1.6 m/s² while g_earth = 10 m/s². Thus weight on moon is 1/6 of weight on Earth.
Q3. A body weighs 50 N on Earth. What is its mass? (g = 10 m/s²)
Weight W = mg. So m = W/g = 50/10 = 5 kg. The mass remains 5 kg anywhere (on Earth, moon, space).
Q4. State the universal law of gravitation.
Every object attracts every other object with force proportional to product of their masses and inversely proportional to square of distance between them. Mathematically: F = G(m1 × m2)/r², where G is gravitational constant.
Q5. If Earth's mass is 6 × 10^24 kg and radius is 6.4 × 10^6 m, calculate g at Earth's surface.
g = GM/R² = (6.67 × 10^-11)(6 × 10^24)/(6.4 × 10^6)² = (40 × 10^13)/(41 × 10^12) ≈ 9.76 m/s² ≈ 10 m/s².
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.