Upthrust in Fluids Archimedes Principle and Floatation Class-9 Exe-5C MCQs Concise Physics ICSE Selina Solutions Ch-5. In this article you would lean to solve MCQs on Floatation. Visit official Website CISCE for detail information about ICSE Board Class-9 Physics.
Upthrust in Fluids Archimedes Principle and Floatation Class-9 Exe-5C MCQs Concise Physics ICSE Selina Solutions Ch-5
| Board | ICSE |
| Class | 9 |
| Subject | Physics |
| Writer / Publication | Concise Selina Publishers |
| Chapter-5 | Upthrust in Fluids, Archimedes’ Principle and Floatation |
| Exe – 5C | Floatation |
| Topics | Solution of Exe-5(C) MCQs Type |
| Academic Session | 2025-2026 |
Floatation
Upthrust in Fluids Archimedes Principle and Floatation Class-9 Exe-5C MCQs Concise Physics ICSE Selina Solutions Ch-5
Page 135 (Choose the correct answer from the option given below).
Que-1: For a floating body, its weight W and upthrust FB on it are related as:
(a) W > FB
(b) W < FB
(c) W = FB
(d) nothing can be said
Ans: (c) W = FB
Hint- When W = FB i.e., the weight of the body is equal to the weight of the displaced liquid then the body will float.
Que-2: The upthrust is maximum (= FB) when the body is:
(a) floating in the liquid
(b) completely immersed inside the liquid
(c) partially immersed inside the liquid
(d) None of these
Ans: (b) completely immersed inside the liquid
Hint- As FB = volume of submerged part of body x density of liquid x g
Hence, FB will be maximum when the body is completely immersed inside the liquid.
Que-3: When the weight of a body is greater than the weight of the liquid displaced, the body will
(a) float
(b) sink
(c) float partially outside
(d) first go down then come up
Ans: (b) sink
Hint- Two forces act on a body immersed in a liquid:
- weight of the body acting vertically downwards and
- upthrust acting vertically upwards
Upthrust is equal in magnitude to the weight of the liquid displaced. When weight of a body is greater than the weight of the liquid displaced, implies downwards force is more than the upwards force, hence the body sinks.
Page 136
Que-4: A body weighing W floats partially above and partially below the liquid when (F‘B denotes maximum upthrust) :
(a) W > F‘B
(b) W = F‘B
(c) W < F‘B
(d) none of these
Ans: (c) W < F‘B
Hint- When a body weighing W floats partially above and partially below the liquid, it implies that the weight of the body is less than the maximum upthrust experienced by it when fully immersed inside the liquid. Hence, W < F‘B.
Que-5: A body of weight W is floating in a liquid. Its apparent weight will be:
(a) equal to W
(b) less than W
(c) greater than W
(d) zero
Ans: (d) zero
Hint- When W = FB i.e., the weight of the body is equal to the weight of the displaced liquid then the body will float and the apparent weight is equal to zero.
Que-6: For a floating body of volume V, the relation between the volume of its submerged part vv, the densities of liquid (ρL) and the body (ρS) is :
Que-7: A body floats in a liquid A of density ρ1 with a part of it submerged inside liquid while in liquid B of density ρ2 totally submerged inside liquid. The densities ρ1 and ρ2 are related as:
(a) ρ1 = ρ2
(b) ρ1 < ρ2
(c) ρ1 > ρ2
(d) nothing can be said
Ans: (c) ρ1 > ρ2
Hint- Density of liquid A ( ρ1) is greater than the density of liquid B ( ρ2) as the body is partially immersed in liquid A whereas it is fully immersed in liquid B.
Que-8: Every ship has a white line painted on its side known as :
(a) Plimsoll line
(b) Border line
(c) Harbour line
(d) None of the above
Ans: (a) Plimsoll line
Hint- Plimsoll line indicates the safe limit for loading the ship in water of density 103 kg m-3. A ship is not allowed to load further if its plimsoll line starts touching the water level, so that when it sails in sea water of density more than 103 kg m-3, only the part of it below the plimsoll line remains submerged in water.
Que-9: Which of the following statements is correct ?
(i) A loaded ship is submerged more while an unloaded ship is submerged less.
(ii) A ship begins to be less submerged as it sails from sea water to river water.
(a) only (i)
(b) only (ii)
(c) both (i) and (ii)
(d) both are incorrect
Ans: (a) only (i)
Hint- A loaded ship is submerged more while an unloaded ship is submerged less because loaded ship has more weight and exerts more force vertically downwards.
A ship begins to be submerged more as it sails from sea water to river water. The water of a river is of low density than that of a sea. Therefore, a ship sails from sea water to river water, it sinks further. The reason is that according to the law of floatation, to balance the weight of ship, a greater volume of water is required to be displaced in water of lower density in river.
Que-10: An unloaded ship is filled with sand at its bottom to …………… its centre of gravity and make its equilibrium ……………
(a) lower, unstable
(b) higher, stable
(c) lower, stable
(d) higher, unstable
Ans: (c) lower, stable
Hint- An unloaded ship floats with very small volume inside water. As a result, its centre of gravity is higher and its equilibrium is unstable. There is a danger that it may get blown over on its side by strong winds. Therefore, an unloaded ship is filled with sand (or stones), called ballast, at its bottom. This lowers its centre of gravity to make its equilibrium stable.
Que-11: It is easier for humans to swim in sea water than in river water as :
(a) the density of sea water is less than that of the river water.
(b) the density of sea water is more than that of river water.
(c) the sea is big in comparison to the river.
(d) None of the above
Ans: (b) the density of sea water is more than that of river water
Hint- It is easier to swim in sea water because the density of sea water is more than that of the river water, so our weight is balanced in sea water with less part of the body submerged inside it.
Que-12: If a submarine is to dive, its ballast tanks are ……………, so that the average density of the submarine becomes …………… than the density of sea water.
(a) filled with water, greater
(b) filled with water, lower
(c) emptied, greater
(d) emptied, lower
Ans: (a) filled with water, greater
Hint- If a submarine is to dive, its ballast tanks are, filled with water so that the average density of the submarine becomes greater than the density of sea water
Que-13: Ice bergs float on the surface of water with their …………… portion inside the water surface and …………… portion above the water surface.
(a) smaller, larger
(b) larger, equal
(c) smaller, smaller
(d) larger, smaller
Ans: (d) larger, smaller
Hint- As ice bergs are lighter than water, they float on the surface of water with their larger portion inside the water surface and smaller portion above the water surface.
Que-14: A balloon does not rise indefinitely because :
(a) the density of air increases with altitude
(b) the density of air decreases with altitude
(c) the weight of the displaced air increases.
(d) None of the above
Ans: (b) the density of air decreases with altitude
Hint- A balloon does not rise indefinitely because the density of air decreases with altitude. Therefore, as the balloon gradually goes up, the weight of the displaced air decreases. It keeps on rising as long as the upthrust on it exceeds its weight. When upthrust becomes equal to its weight, it stops rising further.
Que-15: When a fish has to rise up in water, it diffuses oxygen gas from its blood into the bladder, so its volume …………… and its average density …………… .
(a) decreases, decreases
(b) increases, decreases
(c) decreases, increases
(d) increases, increases
Ans: (b) increases, decreases
Hint- When a fish has to rise up in water, it diffuses oxygen gas from its blood into the bladder, so its volume increases and its average density decreases
This increases the volume of water displaced by the fish and so the upthrust on the fish increases due to which it rises up.
— : End of Upthrust in Fluids Archimedes Principle and Floatation Class-9 Exe-5C MCQs Concise Physics ICSE Selina Solutions :–
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