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PHYSICS [1 Mark Question Answer]

Upthrust in Fluids, Archimedes' Principle and Floatation · ICSE STD 9 (ICSE - English Medium). 20 questions.

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[1 Mark Question Answer]

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20 questions · timed · auto-graded

Question 11 Mark
A homogeneous block floats on water $(a)$ partly immersed $(b)$ completely immersed. In each case state the position of centre of buoyancy $B$ with respect to the centre of gravity $G$ of the block.
Answer
When the body is partially immersed, its centre of buoyancy will be below the centre of gravity of the block. When the body is completely immersed, its centre of buoyancy will coincide the centre of gravity.
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Question 21 Mark
A body floats in a liquid with a part of it submerged inside the liquid. Is the weight of floating body greater than, equal to or less than the upthrust?
Answer
When the body floats then weight of the body is equal to the upthrust acting on the body.
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Question 31 Mark
A solid iron ball of mass $500\ g$ is dropped in mercury contained in a beaker. $(a)$ Will the ball float or sink? Give reasons. $(b)$ What will be the apparent weight of the ball?
Answer
$(a)$ The ball will float because the density of ball $($i.e. iron$)$ is less than the density of mercury.
$(b)$ While floating, the apparent weight $= 0.$
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Question 41 Mark
When a piece of wood is suspended from the hook of a spring balance, it reads $70\ gf.$ The wood is now lowered into water. What reading do you expect on the scale of spring balance?
Answer
The reading on the spring balance will be zero because wood floats on water and while floating the apparent weight $= 0.$
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Question 51 Mark
What can you say about the average density of a ship floating on water in relation to the density of water?
Answer
Due to the hollow and empty space in the ship, the average density of a ship is less than the density of water.
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Question 61 Mark
What do you understand by the term relative density of a substance?
Answer
The relative density of a substance is the ratio of density of that substance to the density of water at $4^\circ C .$
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Question 71 Mark
Water is heated from $0^\circ C$ to $10^\circ C .$ How does the density of water change with temperature?
Answer
On heating from $0^\circ C ,$ the density of water increases up to $4^\circ C$ and then decreases beyond $4^\circ C .$
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Question 81 Mark
Write the density of water at $4^{\circ} C$ in $S.I.$ unit .
Answer
Density of water at $4^{\circ} C$ in $S.I.$ units is $1000\ kg\ m ^{-3}$.
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Question 91 Mark
'The density of iron is $7800\ kg\ m ^{-3}$. What do you understand by this statement?
Answer
It means the mass of $1\ m^{-3}$ of iron is $7800\ kg .$
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Question 101 Mark
Express the relationship between the $C.G.S$. and $S.I.$ units of density.
Answer
$1\ g\ cm ^{-3}=1000\ kg\ m ^{-3}$
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Question 111 Mark
What are the units density in $(i)\ C.G.S$. and $(ii)\ S.I.$ system .
Answer
$(i)$ The $C.G.S.$ unit of density is $g / cm ^3. (ii)$ The $S.I.$ unit of density is $kg / m ^3$.
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Question 131 Mark
Differentiate between density and relative density of a substance.
Answer
Density of a substance is the ratio of its mass to its volume but $R.D.$ of a substance is the ratio of density of that substance to the density of water at $4^\circ C .$
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Question 141 Mark
What is the unit of relative density?
Answer
Relative density is the ratio of two similar quantities; thus, it has no unit.
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Question 151 Mark
Will a body weigh more in air or vacuum when weighed with a spring balance? Give a reason for your answer.
Answer
A body shall weigh more in vacuum because in vacuum, i.e. in absence of air, no upthrust will act on the body.
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Question 161 Mark
A piece of wood if left under water comes to the surface. Explain the reason.
Answer
A piece of wood if left under water comes to the surface of water because the upthrust on body due to its submerged part is equal to its own weight.
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Question 171 Mark
Define upthrust and state its $S.I.$ unit.
Answer
The upward force exerted on a body by the fluid in which it is submerged is called the upthrust. Its $S.I.$ unit is 'newton'.
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Question 181 Mark
What is meant by the term buoyancy?
Answer
The property of a liquid to exert an upward force on a body immersed in it is called buoyancy.
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Question 191 Mark
In what direction and at what point does the buoyant force on a body due to a liquid act?
Answer
Buoyant force on a body due to a liquid acts upwards at the centre of buoyancy.
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Question 201 Mark
How is the upthrust related to the volume of the body submerged in a liquid?
Answer
Larger the volume of body submerged in liquid, greater is the upthrust acting on it.
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