CBSE Class 9 Physics Chapter 9 Gravitation — 20 MCQs with Answers

Newton's law of universal gravitation is the foundation of this chapter. It states that every object in the universe attracts every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres. The formula F = G(m₁m₂)/r² must be memorized, along with the value of G and its SI unit. Students often confuse G (the universal gravitational constant, roughly 6.67 × 10⁻¹¹ N·m²/kg²) with g (acceleration due to gravity, roughly 9.8 m/s²). Questions in this section test your grasp of the law's statement, the inverse-square relationship, and correct substitution into the formula. Pay special attention to units: force in Newtons, mass in kilograms, distance in meters. A common exam trick is to give the distance in centimeters or kilometers and expect you to convert it first.

Mass is an intrinsic property of matter measured in kilograms; it does not change whether you are on Earth, the Moon, or floating in space. Weight, however, is the gravitational force acting on that mass, calculated by W = mg, where g is the local acceleration due to gravity. On Earth g ≈ 9.8 m/s² (often rounded to 10 m/s² in CBSE numericals), but on the Moon g is about one-sixth of Earth's value, roughly 1.6 m/s². A 60 kg student has a weight of 60 × 10 = 600 N on Earth but only 60 × 1.6 = 96 N on the Moon. The mass remains 60 kg in both places. CBSE loves to ask 'What happens to your weight on the Moon?' or 'Why do astronauts feel weightless?' (Answer: they are in free fall, not because gravity is absent.) These MCQs test whether you can distinguish mass from weight and apply W = mg correctly, including unit conversions.

The acceleration due to gravity g is the rate at which any freely falling object accelerates near Earth's surface, approximately 9.8 m/s² (or 10 m/s² for simplified calculations). The value of g is not universal; it varies with location. It is slightly less at the equator than at the poles because Earth is an oblate spheroid (bulges at the equator) and because of the centrifugal effect of Earth's rotation. As you climb a mountain or go higher in altitude, g decreases because you are farther from Earth's centre. Conversely, if you descend into a mine shaft, g also decreases because part of Earth's mass is now above you. The formula for variation with height (for small h) is g_h ≈ g(1 – 2h/R), where R is Earth's radius. Questions here test your ability to predict how g changes and to apply g in kinematic equations like v = u + gt or s = ut + ½gt². Remember: g is always taken as positive 9.8 m/s² or 10 m/s² unless the question specifies another celestial body.

Free fall describes motion under gravity alone, with no other forces like air resistance or thrust. In true free fall, all objects—regardless of their mass—accelerate at the same rate g. This counterintuitive fact puzzled scholars for centuries until Galileo and Newton clarified it. A hammer and a feather dropped together in a vacuum (like on the Moon, famously demonstrated by astronaut David Scott during Apollo 15) hit the ground simultaneously. The reason: although the hammer experiences a larger gravitational force (because it has more mass), it also has greater inertia (resistance to acceleration). These two effects exactly cancel, leaving the same acceleration g for both. On Earth, air resistance complicates things—a feather falls slower than a hammer in air because of drag. CBSE often asks assertion-reason questions: 'Assertion: A heavy stone and a light stone fall at the same rate in vacuum. Reason: Acceleration due to gravity is independent of mass.' Both are true, and the reason correctly explains the assertion.

A frequent source of error in exams is mixing up G (the universal gravitational constant) and g (acceleration due to gravity). G is a fundamental constant of nature, approximately 6.67 × 10⁻¹¹ N·m²/kg², and it is the same everywhere in the universe. It appears in Newton's law F = G(m₁m₂)/r². In contrast, g is a local quantity that varies from place to place; on Earth's surface it is about 9.8 m/s², on the Moon about 1.6 m/s², and on Jupiter much larger. The two are related: if you apply F = G(M_Earth × m)/R² to an object of mass m on Earth's surface and also write F = mg, you can derive g = G M_Earth / R². So g depends on the mass and radius of the celestial body, while G is universal. CBSE loves to ask 'Which of the following is constant throughout the universe?' or 'The value of G on the Moon is...' (Answer: same as on Earth, because G is universal). These MCQs check whether you truly understand the conceptual difference.

CBSE Class 9 Physics exams often include one or two numerical-based MCQs in the objective section, especially in sample papers and board-style mock tests. These require you to substitute values into formulae, perform arithmetic (sometimes with scientific notation), and pick the correct option. Common pitfalls include forgetting to square the distance in F = G(m₁m₂)/r², using wrong units (e.g. distance in cm instead of m), or confusing mass with weight. Always write down the given data, identify the formula, substitute carefully, and double-check units. For Chapter 9 Gravitation, typical numericals ask you to calculate gravitational force between two masses, find weight given mass and g, or determine the new value of g at a certain height. Practice these under timed conditions to build speed. Remember: in MCQs, you can often eliminate obviously wrong answers (e.g. if weight must be in Newtons and one option is in kg, discard it immediately).

CBSE has introduced assertion-reason (A-R) type questions in recent years, and they are excellent for testing deep conceptual understanding rather than rote memorization. In an A-R question, you are given two statements: an Assertion and a Reason. You must decide if each is true or false, and if both are true, whether the Reason correctly explains the Assertion. For example: Assertion – 'The weight of an object on the Moon is less than its weight on Earth.' Reason – 'The Moon has less mass than Earth.' Both statements are individually true, and the Reason does explain the Assertion (because g on the Moon is smaller due to lower mass). Mark option (A). If the Reason were 'The Moon has no atmosphere,' that is also true but does not explain why weight is less, so you would mark (B). These questions reward careful reading and logical thinking. For Gravitation, expect A-R questions on why astronauts float, why g decreases with height, why all objects fall at the same rate in vacuum, and the difference between mass and weight.

Practising MCQs from a static page is useful, but real mastery comes when you can ask follow-up questions, clarify doubts instantly, and get step-by-step solutions tailored to your learning pace. That is where CBSETUTOR.ai shines. It is a 24×7 AI tutor designed specifically for CBSE students in Classes 6 to 12, covering every subject including Physics. You can upload a photo of any Gravitation MCQ or numerical problem from your textbook, worksheet, or school test, and the AI will recognize the question and provide a detailed, NCERT-aligned solution within seconds. The explanations use the exact terminology and steps you see in this guide—no generic Internet answers. If you are confused about why option (B) is correct or how to apply F = G(m₁m₂)/r² in a tricky scenario, simply type your doubt and get a clear answer. The AI adapts to your level, offering hints first if you want to try again, or a full solution if you are stuck. The best part: CBSETUTOR.ai costs just ₹999 per month for unlimited questions across all subjects and classes, with a 3-day free trial so you can experience it risk-free. Thousands of students in Delhi, Mumbai, Pune, Bengaluru, and smaller cities are already using it to boost their confidence and scores. Whether you are preparing for a unit test next week or revising for term exams, having an AI tutor in your pocket transforms your study sessions from frustrating to efficient.

Multiple-choice questions in CBSE Physics papers are designed to test both knowledge recall and application. Here is a systematic approach to maximize your score. First, read the question stem carefully—underline keywords like 'increases,' 'decreases,' 'maximum,' 'minimum,' 'on the Moon,' 'in vacuum.' These words often hold the key to the correct answer. Second, before looking at the options, try to recall the relevant formula or concept. For example, if the question is about gravitational force, mentally note F = G(m₁m₂)/r². Third, eliminate obviously wrong answers. If the question asks for a force and one option is in kilograms, discard it. If it asks for the value of G and one option is 9.8, eliminate it (that is g, not G). Fourth, substitute values carefully if it is a numerical question. Write down your working on the margin of the question paper—CBSE allows rough work on the question booklet. Double-check your arithmetic, especially powers of ten. Fifth, for assertion-reason questions, evaluate the Assertion and Reason separately first, then check if the Reason explains the Assertion. Do not assume that if both are true, the answer is automatically (A)—the Reason must logically explain the Assertion. Sixth, manage your time. CBSE typically allocates 1 mark per MCQ, so spend about 1 minute per question. If you are stuck, mark your best guess and move on—come back if time permits. Seventh, avoid changing answers unless you are very sure; your first instinct is often correct. Finally, revise all MCQs if you finish early. Check that you have not misread 'increases' as 'decreases' or missed a 'not' in the question. These strategies, combined with thorough topic understanding and regular practice, will help you score full marks in the MCQ section of Chapter 9 Gravitation and beyond.