Upthrust is equal to the weight of displaced liquid - class-VII
upthrust is equal to the weight of displaced liquid
Questions
A bob's weight is measured by a spring balance. Its volume is $10 cm^3$. In vacuum it measures $80 g$. What does it weigh in water?
- $70 g$
- $80 g$
- $90 g$
- $76 g$
Upthrust due to fluid equals
- Volume of liquid displaced
- Mass of liquid displaced
- Weight of liquid displaced
- None of the above
A ship has volume of $1,50,000 m^3$. It submerges $10%$ in water. Upthrust felt by it equals
- $15 \times 10^6 N$
- $15 \times 10^7 N$
- $15 \times 10^8 N$
- $15 \times 10^5 N$
Consider a cylinder of height $h$ and Cross sectional area $A$ completely submerged in a fluid of density $\rho$. What is upthrust?
- $Ah\rho g$
- $Ah\rho /g$
- $A\rho g$
- $Ah^2 \rho g$
An object having relative density 0.56 is dropped in water. Will it float or sink in water?
- Sink
- Float
- Depends on the density of water
- Unsure
A body of density equal to density of fluid is sinking at speed of $1 m/s$ at $t=0$. What is distance covered by object in $1s$?
- $0.5m$
- $1m$
- $0.75m$
- $0.875m$
Analyse the given statements and choose the correct option.
Statement I: The buoyant force of water on a submerged wooden cube is greater than the buoyant force of water on a steel cube of equal volume.
Statement II: The buoyant force on a body is equal to the weight of the liquid displaced by the body.
- Both statement I and statement II are correct and statement II is the correct explanation of statement I
- Both statement I and statement II are correct, but statement II is not the correct explanation of statement I
- Statement I is correct, but statement II is incorrect
- Statement I is incorrect, but statement II is correct
The reading of a spring balance when a block is suspended from it in air is 60 newton. This reading is changed to 40 newton when the block is fully submerged in water. The specific gravity of the block must be therefore "
- 3
- 2
- 6
- 3/2
The body when immersed fully or partially in a fluid, experiences an upward force, equal to ............. of displaced fluid.
- Mass
- Weight
- Volume
- Area
A solid sphere weighs $40\ N$ in water and $45\ N$ in water and $45N$ in a liquid of density $0.75$. The weigh of sphere in air will be
- $60\ N$
- $53\ N$
- $50\ N$
- $80\ N$
A piece of ice having a stone frozen in its melts in a glass vessel filled with water. How will the level of water in the vessel change when the ice melts?
- The level will rise
- The level will not change
- The level will drop
- Some water will flow out
A metal wire of density $d$ floats, in a liquid of surface tension $\sigma$, in the horizontal position. The maximum radius of the wire so that it may not sink is
- $\sqrt{\dfrac{2\sigma}{\pi d g}}$
- $\sqrt{\dfrac{3\sigma}{\pi d g}}$
- $\sqrt{\dfrac{5\sigma}{\pi d g}}$
- $\sqrt{\dfrac{7\sigma}{\pi d g}}$
A cubical block floating in a liquid with half of its volume immersed in the liquid.when the hole system accelerates downward with an accelerations $g/3$. The fraction of volume immersed in liquid will be
- $1/3$
- $3/8$
- $2/3$
- $3/4$
Two solids $A$ and $B$ floats in a liquid. it is observed that $A$ floats with half its volume immersed an d$B$ floats with $(2/3$ of its volume immersed. Compare the densities of $A$ and $B$ :
- $4:3$
- $2:3$
- $3:4$
- $1:3$
A block wood side 40 cm flods in wateer ina way that it lower fece 5 cm below the free surface or water.
- ${1600 cm{3}}$
- ${64000 cm{3}}$
- ${3000cm{3}}$
- ${40000cm{3}}$
When a ship floats on water :
- it displaces no water
- the mass of water displaced is equal to the mass of the ship
- the mass of water displaced is lesser than the mass of the ship
- the mass of water displaced is greater than the mass of the ship
A boat 3 m long and 2 m wide is floating in a lake. When a man climbs over it, it sinks 1 cm further into water. The mass of the man is:
- 60 kg
- 64 kg
- 70 kg
- 72 kg
Calculate the height $h$ of the portion of the slab the is above the water surface.
- $0.15\ m$
- $0.16\ m$
- $0.17\ m$
- $0.19\ m$
A ball floats on the surface of water in a container exposed to the atmosphere. Volume $V _{1}$ of its volume in inside the water. If the container is now covered and the air is pumped out. Now let $V _{2}$ be the volume now immersed in water. Then
- $V _{1}=V _{2}$
- $V _{1}>V _{2}$
- $V _{2}>V _{1}$
- $V _{2}=0$
A vessel in the shape of a hollow hemisphere surmounted by a cone is held with the axis vertical and vertex uppermost. If it be filled with a liquid so as to submerge half the axis of the cone in the liquid, and the height of the cone be double the radius of its base, find the value of $x$, where the resultant downward thrust of the liquid on the vessel is $x$ times the weight of the liquid that the hemisphere can hold.
- $15/8$
- $1/8$
- $5/8$
- $15/2$
What is the area of the smallest block of ice $0.5\ m$ thick that will just support a man of mass $100\ kg$? The block of ice is floating in fresh water.$\left(SG\ of\ ice\ =0.9\right)$.
- $2m^{2}$
- $4m^{2}$
- $10m^{2}$
- $0.25m^{2}$
A block of ice of density $0.9\ gm\ cc^{-1}$ and of volume $100\ cc$ floats in water. Then volume of ice inside the water
- $10\ cc$
- $90\ cc$
- $50\ cc$
- $9\ cc$
A wooden cube floating in water supports a mass m = 0.2 kg on its stop. When the mass is removed the cube rises by 2 cm. The side of the cube is - (density of water $10^3 kg/m^3$)
- 6 cm
- 12 cm
- 8 cm
- 10 cm
Three cubes of volume $V , V / 4$ and $V / 8$ respectively are immersed in thesame liquid. If the buoyant force exerted on the $3 ^ { rd }$ cube is 40 units. Then
- Buoyant force on $1 ^ { st }$ cube is 80 units.
- Buoyant force on $1 ^ { st }$ cube is 320 units.
- Buoyant force on $2 ^ { nd }$ cube is 80 units.
- Buoyant force on $2 ^ { nd }$ cube is 320 units.
A body of mass $40 kg$ floats on a lake with $5 { cm }$ in water, when another block placed on the block, $7 { cm }$ are submerged, the mass of second block is :
- $20{ kg }$
- $10{ kg }$
- $16{ kg }$
- $13{ kg }$
A solid sphere weighs $40 N$ in water and $45 N$ in a liquid of relative density $0.7$5 when completely immersed. The weight of sphere in air will be
- $50N$
- $53N$
- $80N$
- $60N$
An ice block contains a glass ball when the ice melts within the water containing vessel, the level of water
- Rises
- Falls
- Unchanged
- First rises and then falls
A body is floating in liquid with $50%$ of its volume out side the liquid. When the entire system accelerates upwards with an acceleration $g / 3 ,$ the percentage of its volume outside the liquid is
- $33 \%$
- $50 \%$
- $25 \%$
- $66 \%$
Ice pieces are floating in a beaker A containing water and also in a beaker B containing miscible liquid of specific gravity 1.2 When ice melts,the level of
- Water increases in A
- Water decreases in A
- Liquid in B decreases
- Liquid in B increases
A body floats in a liquid if the buoyant force is
- zero
- less than its weight
- equal to its weight
- none of these
A block of wood floats in water with (2/3)rd its volume submerged. The density of wood is
- ${ 67gm/cm^{ 3 } }$
- ${ 6.7gm/cm^{ 3 } }$
- ${0. 67gm/cm^{ 3 } }$
- $7\times { 10 }^{ 3 }kg/{ m }^{ 3 }$
Initially A cubical block of density $\rho$ is floating in water. in a vessel Out of its height $L ,$ length $x$ is submerged in water. Suddenly vessel is kept in an elevator accelerating upwards with acceleration $a.$ What is the length immersed in water?
- $L - X$
- $2 x$
- $x$
- $L$
A ball falls through a liquid at a constant speed. It is acted upon by three forces: an upthrust, a drag-force and its weight.
Which statement is correct?
- The drag-force increases with increasing depth
- The drag-force is equal to the sum of the upthrust and weight
- The upthrust is constant with increasing depth
- The weight is greater than the sum of the drag-force and the upthrust
A cube of wood supporting $200g$ mass just floats in water. When the mass is removed, the cube rises by $1cm$, the linear dimension of cube is:
- $10cm$
- $20cm$
- $10\sqrt{2}cm$
- $5\sqrt{2}cm$
A boat having a length of 3 metre and breadth 2 metre is floating on a lake. The boat sinks by one cm when a man gets on it. The mass of the man is:
- 60 kg
- 62 kg
- 72 kg
- 128 kg
A piece of iron of density $7800kg/m^3$ and volume $100cm^3$ is completely immersed in water. Calculate the upthrust on the iron piece.
- $1N$
- $2.8N$
- $7.8N$
- $6.8N$
if a block of wood is floating in a river water, then the apparent weight of the floating block is
- equal to the weight of the displaced water
- zero.
- greater than the weight of the displaced water
- equal to the actual weight of the block
A body of mass 50 kg has a volume 0.049 $m^3$ and is kept on a table. The buoyant force on it due to air is.
- 0.588 N
- 0.49 N
- 58.8 N
- 49 kgf
Calculate the upthrust acting on a ball of volume $\displaystyle 0.2{ m }^{ 3 }$ immersed in a liquid having density $\displaystyle { 1kg }/{ { m }^{ 3 } }$.
- 0.2f
- 2f
- 0.2g f
- 2g f
A cube of wood floats in water, with $42$% of its volume is submerged, then the density of the wood is
- $42\ g\ cm^{-3}$
- $0.42\ g\ cm^{-3}$
- $0.58\ kg\ cm^{-3}$
- $600\ g\ cm^{-3}$
A: Diver dives in and reaches a depth of 100m.
B: Diver swims up from the depth of 100m to the surface.
Choose the correct alternative:
- A is easier than B
- B is easier than A
- A and B are equally hard
- A is easier than B if speed of descent and ascent is same and more.
Mathematical proof of upthrust is based on
- Definition of pressure
- Weight of object
- Pressure exerted by a column of fluid
- Viscosity