What do you understand by the term upthrust of a fluid? Describe an experiment to show its existence.
Will a body weigh more in the air or in vacuum when weighed with a spring balance? Give a reason for your answer
A metal solid cylinder tied to a thread is hanging from the hook of a spring balance. The cylinder is gradually immersed into water contained in a jar. What changes do you expect in the readings of spring balance? Explain your answer
A body dipped into a liquid experience an upthrust. State two factors on which upthrust on the body depends
A bunch of feathers and a stone of the same mass are released simultaneously in the air. Which will fall faster and why? How will your observation be different if they are released
simultaneously in a vacuum?
A body experiences an upthrust F1 in river water and F2 in seawater when dipped up to the same level. Which is more F1 or F2? Give reason
A small block of wood is held completely immersed in
(ii) glycerine, and then released. In each case, what do you observe? Explain the difference in your observation in the
body of volume V and density ρ is kept completely immersed in a liquid of density ρL. If g id the acceleration due to gravity, write expressions for the following:
(i) The weight of the body
(ii) The upthrust on the body
(iii) The apparent weight of the body in liquid
(iv) The loss in weight of the body.
A body held completely immersed inside a liquid experiences two forces:
(i) F1, the force due to gravity, and
(ii) F2, the buoyant force. Draw a diagram showing the direction of these forces backing on the body and state the conditions when the body will float or sink.
Complete the following sentences:
(a) Two balls, one of iron and the other of aluminum experience the same upthrust when\ dipped completely in water if ________________
(b) An empty tin container with its mouth closed has an average density equal to that of a liquid. The container is taken 2m below the surface of that liquid and is left there. Then the container will ___________
(c) A piece of wood is held under water. The upthrust on it will be ___________ the weight of the wood piece
Prove that the loss in weight of a body when immersed wholly or partially in a liquid is equal to the buoyant force (or upthrust) and this loss is because of the difference in pressure exerted by the liquid on the upper and lower surfaces of the submerged part of the body
A sphere of iron and another of wood of the same radius are held underwater. Compare the, upthrust on the two spheres.
[Hint: Both have equal volume inside water.]
A sphere of iron and another of wood, both of the same radius are placed on the surface of the water.
State which of the two will sink? Give a reason for your answer
A body of density ρ is immersed in a liquid of density ρL. State condition when the body will
(ii) sink, in liquid.
A body will experience minimum upthrust when it is completely immersed in:
body of density ρ sinks in a liquid of density ρL. The densities ρ and ρL are related as:
(a) ρ = ρL
(b) ρ < ρL
(c) ρ > ρL
(d) nothing can be said
A body of volume 100cm3 weighs 5kgf in air. It is completely immersed in a liquid of
density 1.8 x 103 kg m-3, find: (i) the upthrust due to liquid and (ii) the weight of the body in liquid
A body weighs 450 gf in air and 310 gf when completely immersed in water. Find:
(i) The volume of the body,
(ii) The loss in weight of the body, and
(iii) The upthrust on the body.
State the assumption made in part (i).
You are provided with a hollow iron ball A of volume 15cm3 and mass 12g and a solid iron ball B of mass 12g. Both are placed on the surface of water contained in a large tub.
Find upthrust on each ball. (b) Which ball will sink? Give reason for your answer.(Density of iron = 8.0 gcm-3)
A solid of density 5000kgm-3 weighs 0.5kgf in air. It is completely immersed in water of density 1000 kg m-3. Calculate the apparent weight of the solid in water
Two spheres A and B, each of volume 100cm3 are placed on water (density =1.0g cm-3). The sphere A is made of wood of density 0.3g cm-3 and sphere B is made of iron of density 8.9g cm-3.
(a) Find: (i) the weight of each sphere, and (ii) the upthrust on each sphere.
(b) Which sphere will float? Give reason
The mass of a block made of a certain material is 13.5kg and its volume is 15 x 10-3 m3.
(a) Calculate upthrust on the block if it is held fully immersed in water
(b) Will the block float or sink in water when released? Give the reason for your answer
(c) What will be the upthrust on the block while floating? Take the density of water = 1000 kg m-3.
A piece of brass weighs 175gf in air and 150 gf when fully immersed in water. The density of water is 1.0gcm-3. (i) What is the volume of the brass piece? (ii) Why does the brass piece
weigh less in the water?
A metal cube of edge 5cm and density 9.0 gcm-3 is suspended by a thread so as to be completely immersed in a liquid of density 1.2 cm-3. Find the tension in the thread.
(Take g = 10 m/s2)
[Hint: Tension in thread = apparent weight of the cube in liquid
A block of wood is floating on water with its dimensions 50cm x 50 cm x 50 cm inside water.
Calculate the buoyant force acting on the block. Take g = 9.8N kg-1.
How are the (i) mass, (ii) volume, and (iii) density of a metallic piece affected, if at all, with increase in temperature?
Complete the following sentences:
(i) Mass = _________ x density
(ii) S.I. unit of density is ___________
(iii) Density of water is _______ kg m-3
(iv) Density in kg m-3 = ________ x density in g cm-3
With the use of Archimedes’ principle, state how you will find the relative density of a solid denser than water and insoluble in it. How will you modify your experiment if the solid is soluble in water?
A body weighs W gf in air and W1 gf when it is completely immersed in water. Find:
(I) volume of the body, (ii) upthrust on the body, (iii) relative density of the material of the body
A body weighs W1 gf in air and when immersed in a liquid it weighs W2 gf, while it weighs W3 gf on immersing it in water. Find: (i) volume of the body (ii) upthrust due to liquid (iii)
relative density of the solid and (iv)relative density of the liquid
The relative density of a substance is expressed by comparing the density of that substance with the density of:
Calculate the mass of air in a room of dimensions 4.5m x 3.5m x 2.5m if the density of air at
N.T.P. is 1.3 kg m-3
A piece of stone of mass 113g sinks to the bottom in the water contained in a measuring cylinder and the water level in-cylinder rises from 30ml to 40ml. Calculate R.D. of stone
A body of volume 100cm3 weighs 1 kgf in air. Find: (i) its weight in water and (ii) its relative density.
A body of mass 70kg, when completely immersed in water, displaces 20,000 cm3 of water.
Find: (i) the weight of the body in water and (ii) the relative density of material of the body.
A solid weighs 120gf in air and 105 gf when it is completely immersed in water. Calculate
the relative density of solid.
A solid weighs 32 gf in air and 28.8 gf in water. Find: (i) the volume of solid, (ii) R.D. of solid, and (iii) the weight of solid in a liquid of density 0.9gcm-3.
A body weighs 20gf in air and 18 gf in water. Calculate relative density of the material of
A solid weighs 1.5 kgf in air and 0.9kgf in a liquid of density 1.2 x 103 kg m-3. Calculate R.D. of solid.
jeweler claims that he makes ornament of pure gold of relative density 19.3. He sells a bangle weighing 25.25 gf to a person. The clever customer weighs the bangle when immersed in water and finds that it weighs 23.075 gf in water. With the help of suitable calculations find out whether the ornament is made of pure gold or not.
[Hint: Calculate R.D of the material of bangle which comes out to be 11.6
A piece of iron weighs 44.5 gf in air. If the density of iron is 8.9 x 103 kg m-3, find the weight of the iron piece when immersed in water.
A piece of stone of mass 15.1g is first immersed in a liquid and it weighs 10.9 gf. Then on immersing the piece of stone in water, it weighs 9.7 gf. Calculate:
(a) The weight of the piece of stone in the air,
(b) The volume of the piece of stone,
(c) The relative density of stone,
(d) The relative density of the liquid.
A body is held immersed in a liquid. (i) Name the two forces acting on the body and draw a diagram to show these forces. (ii) State how do the magnitudes of two forces mentioned in part
(i) determine whether the body will float or sink in the liquid when it is released.
(iii) What is the net force on the body if it (a) sinks, (b) floats?
When a piece of wood is suspended from the hook of a spring balance, it reads 70 gf. The word is now lowered into the water. What reading do you expect on the scale of spring balance?
A solid iron ball of mass 500g is dropped in mercury contained in a beaker, (a) Will the ball float or sink? Give reason. (b) What will be the apparent weight of the ball? Give reason
How does the density ρS of a substance determine whether a solid piece of that substance
will float or sink in a given liquid of density ρL?
Explain why an iron nail floats on mercury, but it sinks in water.
[Hint: Density of iron is less than that of mercury but more than that of water]
A body floats in a liquid with a part of it submerged inside liquid. Is the weight of floating
body greater than, equal to or less than upthrust?
A homogenous 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
The figure shows the same block of wood floating in three different liquids A, B, and C of densities ρ1, ρ2, and ρ3 respectively. Which of the liquid has the highest density? Give a reason for your answer
Draw a diagram to show the forces acting on a body floating in water with its some part submerged. Name the forces and show their points of application.
How is the weight of water displaced by the floating body related to the weight of the body itself?
What is center of buoyancy? State its position for a floating body with respect to the centre of gravity of the body.
A balloon filled with helium gas floats in a big closed jar which is connected to an
evacuating pump. What will be your observation, if air from the jar is pumped out? Explain your answer
A block of wood is so loaded that it just floats in the water at room temperature. What change will occur in the state of floatation, if
(a) Some salt is added to water,
(b) Water is heated
A body of volume V and density ρS floats with volume v inside a liquid of density ρL. Show that
Two identical pieces, one of ice (Density=900 kgm-3)and other of wood (density=300 kg m-3) float on water.
(a) Which of the two will have more volume submerged inside water?
(b) Which of the two will experience more upthrust due to water?
A man first swims in sea water and then in river water.
(i) Compare the weights of sea water and river water displaced by him.
(ii) Where does he find it easier to swim and why?
What can you say about the average density of a ship floating on water in relation to the density of water?
A piece of ice floating in a glass of water melts, but the level of water in the glass does not change. Give reason.
[Hint: Ice contracts on melting]
A buoy is held inside water contained in a vessel by tying it with a thread to the base of the vessel. Name the three forces that keep the buoy in equilibrium and state the direction in which each force acts.
Explain the following:
(a) Icebergs floating in the sea are dangerous for ships.
(b) An egg sinks in freshwater but floats in a strong salt solution
(c) A toy balloon filled with hydrogen rises to the ceiling, but if filled with carbon dioxide sinks to the floor
(d) As a ship in the harbor is being unloaded, it slowly rises higher in water
(e) A balloon filled with hydrogen rises to a certain height and then stops rising further.
(f) A ship submerges more as it sails from seawater to river water
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
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
the 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 the liquid. The densities ρ1 and ρ2 are related as:
(a) ρ1 = ρ2
(b) ρ1 < ρ2
(c) ρ1 > ρ2
(d) nothing can be said
A block of wood of mass 24kg floats on water. The volume of wood is 0.032 m3. Find:
(a) The volume of the block below the surface of the water,
(b) The density of the wood.
(density of water = 1000 kg m-3)
A wooden cube of side 10cm has a mass 700g. What part of it remains above the water surface while floating vertically on the water surface?
A piece of wax floats on the brine. What fractions of its volume is immersed?
Density of wax = 0.95 g cm-3, density of brine = 1.1 gcm3
If the density of ice is 0.9 g cm-3, what portion of an iceberg will remain below the surface of the water in a sea? (Density of seawater = 1.1 g cm-3)
A piece of wood of uniform cross-section and height 15cm floats vertically with its height 10cm in water and 12cm in spirit. Find the density of (i) wood and (ii) spirit.
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