CBSE Class 9 Physics Fluid Mechanics MCQs Set 08

Practice MCQs for Class 9 Physics Fluid Mechanics

Access targeted multiple-choice questions for Fluid Mechanics designed to align with the latest CBSE academic syllabus for Class 9 Physics. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

Access Fluid Mechanics Questions and Solutions

View or download the dedicated Fluid Mechanics MCQ resource below. Practicing these 50 objective questions regularly builds familiarity with standard exam patterns and helps secure higher marks in final Physics evaluations.

Multiple Choice Questions

Question 1: By sucking through a straw, a student can reduce the pressure in his lungs to 750 mm of Hg (density = 13.6 g/cm³). Taking atmospheric pressure as 760 mm of Hg, using the straw he can drink water from a glass up to a maximum depth of
(a) 10 cm
(b) 75 cm
(c) 13.6 cm
(d) 1.36 cm
Show Answer & Explanation

Answer: (c) 13.6 cm

Explanation:
1. The pressure difference = 760 − 750 = 10 mm Hg = 1 cm of Hg.
2. The equivalent water column = 1 × 13.6 = 13.6 cm.

Teacher's Note:
1. Convert the Hg column to water by multiplying by 13.6.

Question 2: Two bodies of equal mass with volumes V and 2V are equalised on a balance. The large body is then immersed in oil of density ρ = 0.9 g/cc. What must be the density of the liquid in which the smaller body is simultaneously immersed so as not to disturb the equilibrium of the balance?
(a) 0.9 g/cc
(b) 1.8 g/cc
(c) 0.45 g/cc
(d) 1.35 g/cc
Show Answer & Explanation

Answer: (b) 1.8 g/cc

Explanation:
1. The balance stays in equilibrium if both bodies feel the same buoyant force.
2. Buoyant force on the large body = 0.9 × 2V × g.
3. Buoyant force on the small body = ρ × V × g, so ρ = 1.8 g/cc.

Teacher's Note:
1. Equal masses stay balanced if the upthrusts are equal.

Question 3: An empty balloon weighs W₁. If air equal in weight to W is pumped into the balloon, the weight of the balloon becomes W₂. Suppose the density of air inside and outside the balloon is the same. Then
(a) W₂ = W₁ + W
(b) W₂ = √(W₁W)
(c) W₂ = W₁
(d) W₂ = W₁ − W
Show Answer & Explanation

Answer: (c) W₂ = W₁

Explanation:
1. The air inside has weight W, but the balloon displaces the same volume of outside air, which has exactly weight W.
2. The upthrust cancels the weight of the air inside, so the apparent weight in air is W₁.
3. Hence W₂ = W₁.

Teacher's Note:
1. The inside air is supported by the same air outside.

Question 4: A piece of ice is floating in a jar containing water. When the ice melts, the level of water
(a) rises
(b) falls
(c) remains unchanged
(d) rises or falls depending upon the mass of ice
Show Answer & Explanation

Answer: (c) remains unchanged

Explanation:
1. The floating ice displaces water equal in weight to the ice.
2. The melted ice becomes the same weight of water, which has exactly that volume.
3. The level stays the same.

Teacher's Note:
1. Floating ice displaces its own weight of water.

Question 5: Find the density of a block of wood that floats in water with 0.1 of its volume above water.
(a) 0.9 g/cc
(b) 0.1 g/cc
(c) 1.1 g/cc
(d) 0.09 g/cc
Show Answer & Explanation

Answer: (a) 0.9 g/cc

Explanation:
1. Fraction submerged = 0.9, so weight of wood = weight of water displaced.
2. ρwood × V = 1 × 0.9V, so ρwood = 0.9 g/cc.

Teacher's Note:
1. Density of floating body = fraction submerged × density of liquid.

Question 6: A body of mass 120 kg and density 600 kg/m³ floats in water. What additional mass could be added to the body so that the body will just sink?
(a) 20 kg
(b) 80 kg
(c) 100 kg
(d) 120 kg
Show Answer & Explanation

Answer: (b) 80 kg

Explanation:
1. Volume of the body = 120/600 = 0.2 m³.
2. To just sink, total mass = density of water × volume = 1000 × 0.2 = 200 kg.
3. Additional mass = 200 − 120 = 80 kg.

Teacher's Note:
1. The body just sinks when its average density equals that of water.

Question 7: A body of volume 100 cc floats immersed completely in water contained in a jar. The mass of water and jar before immersion of the body was 700 g. The mass of water and jar after immersion of the body will be
(a) 500 g
(b) 700 g
(c) 100 g
(d) 800 g
Show Answer & Explanation

Answer: (d) 800 g

Explanation:
1. The body displaces 100 cc of water, whose weight is 100 g.
2. The body experiences an upward thrust of 100 g wt and, by Newton's third law, it presses the water with an equal downward force.
3. So the reading becomes 700 + 100 = 800 g.

Teacher's Note:
1. The water gets the reaction to the buoyant force.

Question 8: An ice cube has a stone frozen inside it. The cube floats in a beaker filled with water. When the ice melts, then
(a) there is no change in the level of water
(b) the water level decreases
(c) the water level increases
(d) the water level first increases and then decreases
Show Answer & Explanation

Answer: (b) the water level decreases

Explanation:
1. While floating, the cube displaces water equal to the weight of ice plus stone.
2. After melting, the ice gives water of its own volume only, and the stone sinks displacing just its own volume.
3. The stone displaces less water than it did when floating, so the level falls.

Teacher's Note:
1. A stone displaces less when it sinks than when it floats.

Question 9: A string has tension T when it is holding a solid block below the surface of a liquid (the liquid has a density greater than that of the solid) and the system is at rest. The tension in the string when the system has an acceleration a in the upward direction is
(a) T(1 + g/a)
(b) T(1 − g/a)
(c) T(1 + a/g)
(d) T(1 − a/g)
Show Answer & Explanation

Answer: (c) T(1 + a/g)

Explanation:
1. At rest, T = V(ρliquid − ρsolid)g.
2. With upward acceleration a the effective gravity becomes (g + a) for both the weight and the buoyant force.
3. T' = V(ρliquid − ρsolid)(g + a) = T(1 + a/g).

Teacher's Note:
1. Replace g by g + a in an upward accelerating frame.

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Fluid Mechanics Objective Questions & Solutions for Class 9 Physics

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FAQs

Where can I access latest CBSE Class 9 Physics Fluid Mechanics MCQs Set 08?

You can get most exhaustive CBSE Class 9 Physics Fluid Mechanics MCQs Set 08 for free on StudiesToday.com. These MCQs for Class 9 Physics are updated for the 2026-27 academic session as per CBSE examination standards.

Are Assertion-Reasoning and Case-Study MCQs included in the Physics Class 9 material?

Yes, our CBSE Class 9 Physics Fluid Mechanics MCQs Set 08 include the latest type of questions, such as Assertion-Reasoning and Case-based MCQs. 50% of the CBSE paper is now competency-based.

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Do you provide answers and explanations for CBSE Class 9 Physics Fluid Mechanics MCQs Set 08?

Yes, Physics MCQs for Class 9 have answer key and brief explanations to help students understand logic behind the correct option as its important for 2026 competency-focused CBSE exams.

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