Physics Upthrust in Fluids Exercise5c
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Q1 State the principle of floatation.
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Q2 A body is held immersed in a liquid. (i) Name the two forces acting on 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 liquid when it is released. (iii) What is the net force on body if it (a) sinks, (b) floats?
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Q3 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?
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Q4 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 ball? Give reason.
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Q5 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?
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Q6 Explain why an iron nail floats on mercury, but it sinks in water.
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Q7 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?
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Q8 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 block.
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Q9 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 reason for your answer.
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Q10 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?
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Q11 What is center of buoyancy? State its position for a floating body with respect to the centre of gravity of body.
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Q12 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 jar is pumped out? Explain your answer
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Q13 A block of wood is so loaded that it just floats in 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?
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Q14 A body of volume V and density ρS, floats with volume v inside a liquid of density ρL. Show that 𝐯/ 𝐕 = 𝛒𝐒/ 𝛒𝐋
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Q16 Why is floating ice less submerged in brine than in water?
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Q17 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?
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Q18 An iron nail sinks in water while an iron ship floats on water. Explain the reason.
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Q19 What can you say about the average density of a ship floating on water in relation to the density of water?
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Q20 A piece of ice floating in a glass of water melts, but the level of water in glass does not change. Give reason.
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Q21 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.
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Q22 A loaded cargo ship sails from sea water to river water. State and explain your observation
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Q23 Explain the following:
(a) Icebergs floating in sea are dangerous for ships.
(b) An egg sinks in fresh water, 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 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 sea water to river water.
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Multiple Choice type Questions :
Q1 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
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Q2 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
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Q3 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
Solution :
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