1
In Activity 10.1, the moment the thread is released the stone —
💡 Hint:
The line that meets the circle at one point.
Explanation:
Once the inward force is gone the stone moves along the tangent.
Class 9 · Science · Chapter 10 · बिहार बोर्ड (BSEB)CBSE · NCERT 2026-27
Gravitation
Gravitation
How to use this page:
1. Read — 10.1 thread · 10.2 stone up · 10.3 paper · 10.4 bottle · 10.5 nail · 10.6 cork · 10.7 balance, diagram, worked example, board tip
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- 1 The motion of the Moon — Activity 10.1
- 2 The universal law of gravitation
- 3 Free fall and g — Activities 10.2 and 10.3
- 4 Mass and weight
- 5 Thrust and pressure
- 6 Buoyancy — Activities 10.4, 10.5 and 10.6
- 7 Archimedes and relative density — Activity 10.7
- Chapter winner — every lesson at mastery ★
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📄 PDF download — notes + answer key
The motion of the Moon — Activity 10.1
चन्द्रमा की गति — क्रियाकलाप 10.1 · Section 10.1 · Activity 10.1
The apple, and the Moon tooNotes
An object thrown upward comes back down. The Moon goes around the Earth. Newton asked: if the Earth pulls an apple, can it also pull the Moon?
A stone on a circle can keep a steady speed, but the direction changes at every point. A change of direction is an acceleration. The force for this acceleration points toward the centre. It is called the centripetal force. The moment the thread is released, the stone flies off along the tangent.
The centripetal force that stops the Moon from running off in a straight line is the attraction of the Earth. The apple also pulls the Earth, but the mass of the Earth is so large that its acceleration is not seen. Activity 8.11 of the previous chapter is only a reminder of circular motion. It is not an activity of this chapter.
Activity 10.1 — a stone on a threadActivity
Tie a small stone to one end of a thread. Hold the other end and whirl the stone. The stone moves in a circle. Release the thread. The stone flies off in a straight line along the tangent. Remove the inward force and the circle does not survive.
Worked exampleExample
Question: The apple pulls the Earth. Why does the Earth not rush toward the apple?
Answer: By the third law the forces are equal. By the second law a = F/m. The mass of the Earth is far larger than the apple, so the acceleration of the Earth is negligible.
10-second revision
- Centripetal force acts toward the centre
- Release the thread and the motion is along the tangent
- The attraction of the Earth keeps the Moon
Board tip · BSEBBoard tip
Write both the words tangent and centripetal force. Only “it revolves” stays incomplete.
Board tip · CBSEBoard tip
Join the apple-and-Earth pair to the third law and the second law.
Check your understandingall correct = mastery ★
2
The attraction of the Earth supplies the centripetal force on the Moon.
Explanation:
True — otherwise the Moon would move off in a straight line.
3
The force toward the centre of the circle is called the ______ force.
💡 Hint:
Activity 10.1.
Explanation:
The centripetal force.
4
The apple pulls the Earth, but the Earth is not seen to move, because —
💡 Hint:
a = F/m.
Explanation:
The forces are equal. The Earth has a large m, so a is very small.
5
In Activity 10.1, what is the motion of the stone before and after the thread is released? Add one sentence about the Moon.
Model answer (board format)
Before, the stone moves in a circle and an inward force keeps changing the direction. When the thread is released the stone flies straight along the tangent. The attraction of the Earth keeps the Moon on its path in the same way.
Check your answer:
The universal law of gravitation
सार्वत्रिक गुरुत्वाकर्षण नियम · Section 10.1.1 · F = GMm/d²
Two masses, the square of the distanceNotes
Every object in the universe attracts every other object. The force is proportional to the product of the masses and inversely proportional to the square of the distance. The direction is along the line joining the centres.
F = G M m / d². G is the universal gravitation constant. The accepted value from the measurement of Cavendish is 6.673 × 10⁻¹¹ N m² kg⁻². The law is universal because it applies to small and large bodies, in the sky and on the Earth.
If the distance becomes 6 times, the force becomes 36 times smaller. That is the inverse square. Two friends sitting close feel no such force, because it is tiny. Only a large mass makes the force show up in daily life. The law binds us to the Earth and explains the motion of the Moon, the motion of the planets and the tides.
Worked exampleExample
Question: The Earth has mass 6 × 10²⁴ kg, the Moon 7.4 × 10²² kg, and the distance is 3.84 × 10⁸ m. G = 6.7 × 10⁻¹¹ N m² kg⁻². Find the force.
Formula: F = G M m / d²
Substitution: F = (6.7 × 10⁻¹¹ × 6 × 10²⁴ × 7.4 × 10²²) / (3.84 × 10⁸)²
Answer: F = 2.01 × 10²⁰ N.
10-second revision
- F = GMm/d², along the line of centres
- G = 6.673 × 10⁻¹¹ N m² kg⁻²
- If distance ×6, the force is 1/36
Board tip · BSEBBoard tip
Do not forget d² in the formula. If you write d, the inverse square is lost.
Board tip · CBSEBoard tip
If the distance is halved the force becomes 4 times. This ratio comes up often.
Check your understandingall correct = mastery ★
1
If the distance doubles, the gravitational force —
💡 Hint:
1/d².
Explanation:
(2d)² = 4d², so the force becomes 1/4.
2
The unit of G is N m² kg⁻².
Explanation:
True — F d² / (M m) gives this unit.
3
In the universal law, F = G M m / ______.
💡 Hint:
Inverse square.
Explanation:
d².
4
If one mass is doubled, the force —
💡 Hint:
F is proportional to M m.
Explanation:
The product doubles, so the force doubles.
5
In the Earth-Moon example the force is about —
💡 Hint:
G, M, m and d².
Explanation:
F = 2.01 × 10²⁰ N.
6
State the universal law. If the distance is halved, by what factor does the force change? Give the reason in one line.
Model answer (board format)
The force is proportional to the product of the masses and inversely proportional to the square of the distance, F = GMm/d². If the distance is halved, d² becomes one quarter, so the force becomes 4 times.
Check your answer:
Free fall and g — Activities 10.2 and 10.3
मुक्त पतन और g — क्रियाकलाप 10.2 और 10.3 · Section 10.2 · g = 9.8 m s⁻²
Activities 10.2 and 10.3Activity
10.2 Throw a stone upward. It reaches a height and then starts falling. Falling under the gravity of the Earth alone is free fall. The direction does not change, the speed does, so there is an acceleration. That acceleration is g.
10.3 Drop a sheet of paper and a stone together. The paper arrives later, because air friction on the paper is larger. In a jar from which the air has been removed, both fall together. The story of Galileo at Pisa says the same thing.
g does not depend on the massNotes
The force on the stone is F = m g. For the Earth, g = G M / R². With M = 6 × 10²⁴ kg, R = 6.4 × 10⁶ m and G = 6.7 × 10⁻¹¹ N m² kg⁻², g = 9.8 m s⁻². The falling mass is not in this formula, so hollow or solid, large or small, the acceleration is the same.
Near the Earth, write g in place of a in the equations of uniform acceleration: v = u + gt, s = ut + ½ gt², v² = u² + 2gs. Take the acceleration as positive along the velocity and negative when it opposes the motion. g falls a little with height and toward the equator.
Worked exampleExample
Question: A car falls off a ledge and reaches the ground in 0.5 s. Take g = 10 m s⁻². Find the speed and the distance.
Formula: v = u + gt and s = ut + ½ gt². u = 0.
Substitution: v = 0 + 10 × 0.5 = 5. s = 0 + ½ × 10 × (0.5)² = 5 × 0.25.
Answer: v = 5 m s⁻¹ downward, s = 1.25 m.
10-second revision
- g = GM/R² = 9.8 m s⁻²
- Remove the air and paper and stone fall together
- For 0.5 s and g = 10, s = 1.25 m
Board tip · BSEBBoard tip
The unit of g is m s⁻², not the newton. The newton is the unit of weight.
Board tip · CBSEBoard tip
If the paper falls late, write air as the reason, not the mass.
Check your understandingall correct = mastery ★
1
Near the surface of the Earth, g is —
💡 Hint:
The unit of acceleration.
Explanation:
g = 9.8 m s⁻².
2
In a vacuum a sheet of paper and a stone fall at the same rate.
Explanation:
True — once air resistance is gone, mass does not change the rate.
3
g = G M / ______.
💡 Hint:
The square of the radius of the Earth.
Explanation:
R².
4
A stone is released from rest from a tower 19.6 m high. Find the speed at the ground. g = 9.8 m s⁻². Write the formula, the substitution and the unit.
Model answer (board format)
Formula v² = u² + 2gs. u = 0. v² = 2 × 9.8 × 19.6 = 384.16. v = 19.6 m s⁻¹ downward.
Check your answer:
Mass and weight
द्रव्यमान और भार · Sections 10.3 and 10.4 · W = mg
One stays, one changesNotes
Mass is the measure of inertia. It does not change on the Earth, the Moon or in space. Weight is the force with which the Earth pulls the object.
W = m g. The unit is the newton and the direction is vertically downward. Where g is constant, weight is proportional to mass, so a balance that seems to read mass is really measuring weight.
The mass of the Moon is less than the mass of the Earth. From the universal law, weight on the Moon comes out about 1/6 of the weight on the Earth. The mass does not change.
| Point | Mass | Weight |
|---|---|---|
| What it is | Measure of inertia | Gravitational force |
| Unit | kg | N |
| If the place changes | Does not change | Changes with g |
Worked exampleExample
Question: An object has mass 10 kg. Find the weight on the Earth, g = 9.8 m s⁻². What is the weight on the Moon?
Formula: W = m g, and on the Moon W_m = W / 6.
Substitution: W = 10 kg × 9.8 m s⁻² = 98 N. W_m = 98 / 6.
Answer: 98 N on the Earth, about 16.3 N on the Moon. The mass is 10 kg in both places.
10-second revision
- Mass in kg, free of the place
- W = mg, unit N, downward
- Weight on the Moon ≈ 1/6
Board tip · BSEBBoard tip
Even if a balance shows kg, write that it is calibrated from weight.
Board tip · CBSEBoard tip
If the Earth weight is 10 N, the Moon weight is 10/6 = 1.67 N. Do not forget the fraction.
Check your understandingall correct = mastery ★
1
What does not change on the Moon —
💡 Hint:
The measure of inertia.
Explanation:
Mass does not change. Weight becomes about 1/6.
2
Weight is a force and its unit is the newton.
Explanation:
True — W = mg.
3
The weight of a 10 kg object on the Earth is ______ N when g = 9.8 m s⁻².
💡 Hint:
W = mg.
Explanation:
98 N.
4
An object that weighs 10 N on the Earth weighs on the Moon —
💡 Hint:
1/6.
Explanation:
10/6 = 1.67 N.
5
Write three differences between mass and weight.
Model answer (board format)
Mass is the measure of inertia, a scalar, unit kg, and it does not change with place. Weight is the gravitational force, a vector, unit newton, and it changes with g. W = mg.
Check your answer:
Thrust and pressure
प्रणोद और दाब · Section 10.5 · pascal
Not the force, the force per areaNotes
A pointed pin enters a board more easily. Standing, your feet sink into sand. Lying down, the body does not sink as much. In both cases the force is your weight.
The force perpendicular to a surface is called thrust. Pressure = thrust / area. The SI unit is N m⁻², called the pascal (Pa). A smaller area gives a larger pressure. That is why a nail has a point, a knife has an edge, and a building has a wide foundation.
Liquids and gases are fluids. In a confined fluid, pressure is transmitted undiminished in every direction.
Worked exampleExample
Question: A wooden block of 5 kg is 40 cm × 20 cm × 10 cm. Find the pressure on the 20 cm × 10 cm face and on the 40 cm × 20 cm face. g = 9.8 m s⁻².
Formula: thrust F = m g, pressure = F / area.
Substitution: F = 5 × 9.8 = 49 N. Smaller area = 0.20 × 0.10 = 0.02 m². Larger area = 0.40 × 0.20 = 0.08 m².
Answer: P₁ = 49 / 0.02 = 2450 Pa. P₂ = 49 / 0.08 = 612.5 Pa.
10-second revision
- Thrust = perpendicular force, unit N
- Pressure = thrust / area, unit Pa
- 2450 Pa on the 20 cm × 10 cm face
Board tip · BSEBBoard tip
Change cm² into m² by multiplying by 10⁻⁴. 200 cm² = 0.02 m².
Board tip · CBSEBoard tip
One thrust, two areas. The smaller area gives the larger pressure — write that sentence.
Check your understandingall correct = mastery ★
1
The SI unit of pressure is —
💡 Hint:
N/m².
Explanation:
The pascal. 1 Pa = 1 N m⁻².
2
The same force gives a larger pressure on a smaller area.
Explanation:
True — pressure = force / area.
3
Pressure = thrust / ______.
💡 Hint:
Pa = N/m².
Explanation:
Area.
4
The thrust of a 5 kg block, g = 9.8, is —
💡 Hint:
F = mg.
Explanation:
5 × 9.8 = 49 N.
5
A building foundation is wide so that —
💡 Hint:
The area is larger.
Explanation:
A larger area decreases the pressure and the ground does not sink.
6
Why does a school bag with a thin strap hurt the shoulder? Write it from the definition of pressure.
Model answer (board format)
The weight of the bag is the thrust. A thin strap has a small area, so pressure = thrust/area becomes large and the shoulder hurts.
Check your answer:
Buoyancy — Activities 10.4, 10.5 and 10.6
उत्प्लावन — क्रियाकलाप 10.4, 10.5 और 10.6 · Sections 10.5.2 · 10.5.3
An upward pushNotes
In a pool the body feels light. A bucket feels heavier once it is out of the well. An iron ship floats. The same iron as a sheet can sink. The reason is buoyancy.
An object immersed in a fluid feels an upward force. That force equals the weight of the fluid displaced. If the density of the object is less than the fluid, it floats. If the density is greater, it sinks. Density = mass / volume, unit kg m⁻³.
Activities 10.4, 10.5 and 10.6Activity
10.4 Close an empty plastic bottle with an airtight stopper and put it in a bucket of water. The bottle floats. Push it down. The deeper the push, the larger the upward force, until the bottle is fully immersed. Release it and it returns to the surface. Weight pulls down. Water pushes up.
10.5 Place an iron nail on the surface of water. The nail sinks. The downward weight is greater than the upthrust of the water.
10.6 Take a cork and an iron nail of equal mass. The cork floats and the nail sinks. The density of cork is less than water. The density of the nail is greater.
Worked exampleExample
Question: 50 g of a substance has volume 20 cm³. The density of water is 1 g cm⁻³. Will the object float or sink?
Formula: density = mass / volume.
Substitution: density = 50 g / 20 cm³ = 2.5 g cm⁻³.
Answer: 2.5 is greater than 1 for water, so the object sinks.
10-second revision
- Buoyancy acts upward
- In 10.5 the nail sinks, in 10.6 the cork floats
- Density = mass / volume
Board tip · BSEBBoard tip
Write the float-or-sink decision from density, not only from the words iron or wood.
Board tip · CBSEBoard tip
A ship floats even though it is iron, because the average density stays less than water.
Check your understandingall correct = mastery ★
1
An iron nail sinks in water because —
💡 Hint:
Activities 10.5 and 10.6.
Explanation:
The density of the nail is greater than water, so it sinks.
2
The harder it becomes to push a closed empty bottle deeper, the more the upward force has grown.
Explanation:
True — the upthrust grows until the bottle is fully immersed.
3
Density = mass / ______.
💡 Hint:
The unit is kg m⁻³.
Explanation:
Volume.
4
A cork and an iron nail have equal mass. One floats and one sinks. Write the reason.
Model answer (board format)
The density of cork is less than water, so the upthrust is greater than its weight and it floats. The density of the nail is greater than water, so it sinks.
Check your answer:
Archimedes and relative density — Activity 10.7
आर्किमिडीज़ और आपेक्षिक घनत्व — क्रियाकलाप 10.7 · Sections 10.6 · 10.7 · Activity 10.7
Activity 10.7 — a stone in waterActivity
Hang a stone from a rubber string or a spring balance. Note the extension or the reading in air. Lower the stone slowly into water. The extension of the string, or the reading of the balance, decreases. Once the stone is fully immersed there is no further decrease, because the displaced volume no longer increases.
The extension was due to the weight. The decrease means the water exerts an upward force. That is buoyancy.
The weight of the displaced fluidNotes
A body immersed fully or partly feels an upward force equal to the weight of the fluid displaced. That is the principle of Archimedes. Ships, submarines, lactometers and hydrometers rest on it.
Relative density = density of the substance / density of water. If both densities use the same unit, the ratio has no unit. If the relative density of silver is 10.8 and the density of water is 10³ kg m⁻³, the density of silver is 10.8 × 10³ kg m⁻³.
If a balance reads 42 kg, the buoyancy of air makes the reading a little small, so the real mass is a little more than 42 kg. At the same reading a bag of cotton is really heavier than an iron bar, because the cotton has a larger volume and a larger buoyancy of air.
Worked exampleExample
Question: The relative density of silver is 10.8. The density of water is 10³ kg m⁻³. Find the density of silver in SI.
Formula: density = relative density × density of water.
Substitution: density = 10.8 × 10³ kg m⁻³.
Answer: 1.08 × 10⁴ kg m⁻³. Relative density has no unit.
10-second revision
- Buoyancy = weight of the displaced fluid
- After full immersion the reading falls no further
- Relative density has no unit
Board tip · BSEBBoard tip
In 10.7, answer “why no further decrease” with volume, not with weight.
Board tip · CBSEBoard tip
Do not attach kg or N to an answer that is a relative density.
Check your understandingall correct = mastery ★
1
The upward force of Archimedes equals —
💡 Hint:
The weight of the fluid, not only its volume.
Explanation:
The upward force equals the weight of the displaced fluid.
2
After the stone is fully immersed the balance reading keeps on falling.
Explanation:
False — the displaced volume stops increasing, so there is no further fall.
3
The unit of relative density is ______.
💡 Hint:
A ratio of like quantities.
Explanation:
There is no unit.
4
If the relative density of silver is 10.8, the SI density is —
💡 Hint:
Water is 10³ kg m⁻³.
Explanation:
10.8 × 10³ = 1.08 × 10⁴ kg m⁻³.
5
A balance reads 42 kg. Is the real mass more or less? Write one line using the buoyancy of air.
Model answer (board format)
Air exerts a small upward force, so the reading is a little less than the real weight. The real mass is more than 42 kg.
Check your answer:
❓ Full question bank — with answers and explanations — 67 questions
Pick a type. The 35 lesson checks are separate — each lesson has as many as its topic needs. All correct earns mastery ★.
BSEB modelpractice · not annual60 tried · 0 correctMultiple choiceMCQ140 tried · 0 correctTrue / falseTrue / false80 tried · 0 correctFill in the blanksFill80 tried · 0 correctMatchMatch20 tried · 0 correctAssertion–reasonAssertion–reason50 tried · 0 correctBalancingBalancing40 tried · 0 correctIdentifyIdentify20 tried · 0 correctShort and longVSA, SA, LA120 tried · 0 correctCBSE-stylenot a PYQ60 tried · 0 correct
No question is marked as a verified past paper. The BSEB set is a model for practice. CBSE items are CBSE-style, not a copy of any year’s paper.
Multiple choice
0/14Pick one option. A wrong try brings a hint.
1
When the thread is released the stone moves —
💡 Hint:
Activity 10.1.
Explanation:
Straight motion along the tangent.
2
In F = GMm/d² if the distance becomes three times, the force —
💡 Hint:
(3d)² = 9d².
Explanation:
The force becomes 1/9.
3
The accepted value of G is about —
💡 Hint:
Cavendish.
Explanation:
6.673 × 10⁻¹¹ N m² kg⁻².
4
The acceleration of free fall is called —
💡 Hint:
9.8 near the Earth.
Explanation:
g.
5
Paper falls later than a stone because —
💡 Hint:
Activity 10.3.
Explanation:
Air friction on the paper is larger. In a vacuum both fall together.
6
In W = mg the unit of weight is —
💡 Hint:
The unit of force.
Explanation:
The newton.
7
A weight of 60 N on the Earth is about this on the Moon —
💡 Hint:
1/6.
Explanation:
60/6 = 10 N.
8
Pressure is larger when —
💡 Hint:
P = F/A.
Explanation:
Smaller area, larger pressure.
9
The thrust of 5 kg at g = 9.8 is —
💡 Hint:
mg.
Explanation:
49 N.
10
An iron nail sinks and a cork floats because —
💡 Hint:
Activity 10.6.
Explanation:
Lower density floats, higher density sinks.
11
Relative density —
💡 Hint:
A ratio of like quantities.
Explanation:
There is no unit.
12
The density 50 g / 20 cm³ is —
💡 Hint:
Water is 1 g cm⁻³.
Explanation:
2.5 > 1, so it sinks.
13
For u = 0, t = 0.5 s, g = 10 the distance is —
💡 Hint:
s = ½ gt².
Explanation:
½ × 10 × 0.25 = 1.25 m.
14
A balance reading of 42 kg —
💡 Hint:
The buoyancy of air is upward.
Explanation:
The real mass is a little more than 42 kg.
True or false
0/81
Gravitation acts only between heavy bodies.
Explanation:
False — the law is for all objects. Between light objects the force is very small.
2
g depends on the mass of the falling object.
Explanation:
False — the falling mass is not in g = GM/R².
3
Mass stays the same on the Moon.
Explanation:
True — what changes is the weight.
4
The unit of pressure is the pascal.
Explanation:
True — 1 Pa = 1 N m⁻².
5
Buoyancy acts downward.
Explanation:
False — buoyancy acts upward.
6
The unit of relative density is kg m⁻³.
Explanation:
False — the ratio has no unit. kg m⁻³ is the unit of density.
7
Once a stone is fully immersed, lowering it further keeps increasing the displaced volume.
Explanation:
False — after full immersion the volume does not increase, so the reading stops falling.
8
If both masses are doubled, the gravitational force becomes four times.
Explanation:
True — the product becomes 4 times.
Fill in the blanks
0/81
The centripetal force points toward the ______.
💡 Hint:
The centre.
Explanation:
The centre of the circle.
2
F = ______ M m / d².
💡 Hint:
G.
Explanation:
The universal constant.
3
Near the Earth g = ______ m s⁻².
💡 Hint:
9.8.
Explanation:
GM/R².
4
Weight W = ______.
💡 Hint:
mg.
Explanation:
In newtons.
5
The unit of pressure is the ______.
💡 Hint:
The pascal.
Explanation:
N/m².
6
Density = mass / ______.
💡 Hint:
Volume.
Explanation:
kg m⁻³.
7
The density of silver 10.8 × 10³ = ______ kg m⁻³.
💡 Hint:
10800, or 1.08 × 10⁴.
Explanation:
1.08 × 10⁴.
8
Weight on the Moon is about ______ of the weight on the Earth.
💡 Hint:
1/6.
Explanation:
The mass does not change.
Match
0/21
Match the quantity with the unit.
Column B: A. m s⁻² · B. N · C. Pa · D. N m² kg⁻²
1. G
2. g
3. Weight
4. Pressure
Explanation:
G uses N m² kg⁻², g uses m s⁻², weight uses N, pressure uses Pa.
2
Match the activity with the observation.
Column B: A. Paper falls later · B. The nail sinks · C. The reading falls · D. It flies off on the tangent
1. 10.1 thread
2. 10.3 paper
3. 10.5 nail
4. 10.7 balance
Explanation:
10.1 is the tangent, 10.3 the paper, 10.5 the nail, 10.7 the reading.
Assertion–reason
0/5Check both statements, then see whether the reason explains the assertion.
1
Assertion (A): When the distance doubles, the gravitational force becomes one quarter.
Reason (R): The force is inversely proportional to the square of the distance.
Explanation:
Both are true and R explains A.
2
Assertion (A): In a vacuum a heavy object and a light object fall at the same rate.
Reason (R): g is proportional to the mass of the falling object.
Explanation:
A is true. R is false — g = GM/R² does not depend on the mass.
3
Assertion (A): Weight decreases on the Moon.
Reason (R): Mass is the measure of inertia.
Explanation:
Both are true, but R does not explain why the weight falls. The weight falls because g on the Moon is smaller.
4
Assertion (A): The unit of relative density is kg m⁻³.
Reason (R): Relative density is a ratio of two densities.
Explanation:
A is false. R is true — a ratio has no unit.
5
Assertion (A): An iron nail sinks in water.
Reason (R): The density of the nail is greater than the density of water.
Explanation:
Both are true and R explains A.
Coefficient practice
0/4These equations are not a result of this chapter. This is only coefficient practice for H2 + O2 → H2O.
1
This is coefficient practice 1, not a result of this chapter. Gravitation has no chemical equation. Fill the coefficients of H2 + O2 → H2O.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for water. Do not treat it as a result of this chapter.
2
This is coefficient practice 2, not a result of this chapter. Gravitation has no chemical equation. Fill the coefficients of H2 + O2 → H2O.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for water. Do not treat it as a result of this chapter.
3
This is coefficient practice 3, not a result of this chapter. Gravitation has no chemical equation. Fill the coefficients of H2 + O2 → H2O.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for water. Do not treat it as a result of this chapter.
4
This is coefficient practice 4, not a result of this chapter. Gravitation has no chemical equation. Fill the coefficients of H2 + O2 → H2O.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for water. Do not treat it as a result of this chapter.
Classify
0/21
Place each fact under mass or weight.
Unit kg
W = mg
Does not change on the Moon
About 1/6 on the Moon
Explanation:
The kg and staying constant belong to mass. W = mg and 1/6 belong to weight.
2
Choose float or sink for each object in water.
Iron nail
Cork
Density 2.5 g cm⁻³
Density less than water
Explanation:
The nail and 2.5 g cm⁻³ sink. Cork and a lower density float.
Very short answer
0/51
Write the formula of the universal law.
Model answer (board format)
F = G M m / d².
Check your answer:
2
Define free fall.
Model answer (board format)
When an object falls under the gravitational force of the Earth alone, the motion is free fall. The acceleration is g.
Check your answer:
3
Write one difference between mass and weight.
Model answer (board format)
Mass does not change with place and the unit is the kg. Weight W = mg can change with place and the unit is the newton.
Check your answer:
4
Write the definition and the unit of pressure.
Model answer (board format)
Pressure is thrust per unit area. The SI unit is the pascal, 1 Pa = 1 N m⁻².
Check your answer:
5
State the principle of Archimedes in one line.
Model answer (board format)
The upward force on an immersed body equals the weight of the fluid displaced.
Check your answer:
Short answer
0/41
Find g of the Earth from g = GM/R². G = 6.7 × 10⁻¹¹, M = 6 × 10²⁴ kg, R = 6.4 × 10⁶ m. Write the values and the unit.
Model answer (board format)
g = (6.7 × 10⁻¹¹ × 6 × 10²⁴) / (6.4 × 10⁶)² = 4.02 × 10¹⁴ / 4.096 × 10¹³ = 9.8 m s⁻².
Check your answer:
2
A ball is thrown upward at 49 m/s. g = 9.8 m s⁻². Find the maximum height and the total time to return. Take upward as positive.
Model answer (board format)
At the top v = 0. 0 = 49² + 2(−9.8)s. s = 2401/19.6 = 122.5 m. Time to go up = 49/9.8 = 5 s. Total time to return = 10 s.
Check your answer:
3
The 40 cm × 20 cm face of a 5 kg wooden block rests on a table. Find the pressure. g = 9.8 m s⁻².
Model answer (board format)
Thrust = 5 × 9.8 = 49 N. Area = 0.40 × 0.20 = 0.08 m². Pressure = 49/0.08 = 612.5 Pa.
Check your answer:
4
A bag of cotton and an iron bar both read 100 kg on a balance. Which is really heavier, and why?
Model answer (board format)
The cotton is heavier. Its volume is larger, so the buoyancy of air is larger. For the same reading the real weight, and the mass, of the cotton must be greater than that of the iron.
Check your answer:
Long answer
0/31
State the universal law and give its four uses. Then show why halving the distance makes the force 4 times.
Model answer (board format)
F = GMm/d². Uses: binding us to the Earth, the motion of the Moon, the motion of the planets, and the tides of the Moon and the Sun. If the distance is d/2, each d² is replaced by d²/4. The force is in the ratio 1/(d²/4) = 4/d², that is 4 times.
Check your answer:
2
Compare mass and weight. Find the weight of a 10 kg object on the Earth and on the Moon. g = 9.8 m s⁻² and the Moon weight is 1/6. What would the arrow and the label show in the figure?
Model answer (board format)
Mass is inertia, in kg, constant. Weight is a force, W = mg, in newtons, downward. W = 10 × 9.8 = 98 N. On the Moon 98/6 ≈ 16.3 N. In the figure the label m = 10 kg stays the same in both places, and the downward arrow is 98 N on the Earth and about 16.3 N on the Moon.
Check your answer:
3
What is buoyancy? State the principle of Archimedes. In Activity 10.7, why does the reading fall, and why does it stop after full immersion? Write the condition for floating in terms of density.
Model answer (board format)
Buoyancy is the upward force of a fluid. Archimedes: this force equals the weight of the fluid displaced. Water pushes up, so the balance reading falls. After full immersion the displaced volume does not increase, so there is no further fall. If the density is less than the fluid the object floats. If it is greater, the object sinks.
Check your answer:
BSEB model paper · practice
0/6This model set is for practice. It is not a question from any year’s annual examination.
1
If the distance between two objects is halved, the gravitational force —
💡 Hint:
1/d².
Explanation:
The force becomes 4 times.
2
A heavy object does not fall faster than a light object, because —
💡 Hint:
Both F and m increase.
Explanation:
a = F/m = g, and the mass cancels.
3
The gravitational force between the Earth and an object is called ______.
💡 Hint:
Weight.
Explanation:
W = mg.
4
In what direction does the buoyant force act?
Model answer (board format)
The buoyant force acts upward.
Check your answer:
5
Why does a piece of plastic released under water come up to the surface?
Model answer (board format)
The density of plastic is less than water. The upthrust is greater than its weight, so it rises and floats.
Check your answer:
6
A sealed packet of 500 g has volume 350 cm³. The density of water is 1 g cm⁻³. Will the packet float or sink? Find the density and write it.
Model answer (board format)
Density = 500/350 = 1.43 g cm⁻³. This is greater than 1 g cm⁻³, so the packet sinks.
Check your answer:
CBSE-style questions
0/6These are competency-based practice questions. They are not copies of a CBSE paper.
1
Feet sink in sand when you stand, and less when you lie down. The reason is —
💡 Hint:
Pressure = weight / area.
Explanation:
Larger area, smaller pressure.
2
A student says that on the Moon the mass becomes 1/6. The right correction is —
💡 Hint:
W = mg.
Explanation:
m is constant. W on the Moon is about 1/6.
3
Assertion (A): The tip of a nail is kept sharp.
Reason (R): The same force on a small area gives a large pressure.
Explanation:
Both are true and R explains A.
4
Assertion (A): The upthrust on an object in water acts downward.
Reason (R): By Archimedes this force equals the weight of the fluid displaced.
Explanation:
A is false — buoyancy acts upward. R is true.
5
The same 10 kg sack is in two villages. A balance reads near 98 N at the coast and a little less on a high mountain. Did the mass change, or the weight? What would you tell the farmer?
Model answer (board format)
The mass is still 10 kg. At a height g is a little smaller, so the weight W = mg falls a little. A balance measures weight and is marked in kg, so the reading on the mountain can be a little low. The grain has not decreased.
Check your answer:
6
A boat is made from an iron sheet and it floats. The same sheet, folded into a solid lump, sinks. Explain with density and buoyancy.
Model answer (board format)
The shape of the boat displaces a large amount of water. The average density stays less than water, so the upthrust equals or exceeds the weight and the boat floats. The solid lump has a density greater than water and displaces less water, so it sinks.
Check your answer:
🏛️ Board exam corner — Bihar Board (BSEB)— CBSE
Switch board with BSEB | CBSE above. The lessons follow the same NCERT chapter.
BSEB model · practiceBoard tip
This page has no verified annual-exam question, because no source page has been added. The model set below is practice in the board pattern.
🏛️ Model questions on one page →
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CBSE-style · competency-based
These are case and assertion-reason practice items. Do not treat them as past CBSE questions.
🔁 Spaced review — today’s questions
Wrong questions return soon; correct ones return after a few days.
🧠 What you learned + equation sheet
What you learned
- F = G M m / d². If the distance doubles, the force becomes one quarter.
- Near the Earth g = 9.8 m s⁻², and it does not depend on the falling mass.
- Mass stays constant. Weight is W = mg and can change from place to place.
- Weight on the Moon is about 1/6 of the weight on the Earth.
- Pressure = thrust / area, unit pascal. A smaller area means a larger pressure.
- Buoyancy acts upward and equals the weight of the displaced fluid. Lower density floats, higher density sinks.
| What | Keep this |
|---|---|
| Universal force | F = GMm/d² |
| G | 6.673 × 10⁻¹¹ N m² kg⁻² |
| g | 9.8 m s⁻² near the Earth |
| Weight | W = mg, unit N |
| Moon | weight about 1/6 of Earth |
| Relative density | no unit |
The notes are original writing. The textbook was used only for activity order and numbers. “Verified” will be used only on a question that has a source page.