Very Short Answer Type Questions [1 Mark Each]
Q.1. When a vessel containing a liquid is falling freely, does Archimedes’ principle hold good in it?
Answer
Answer: No – because in fall Buoyant force doesn’t exist.Q.2. A block of wood floats in a bucket of water in a lift. Will there be any change in the equilibrium of wood if the lift starts accelerating upwards?
Answer
Answer: No – because equilibrium of floating bodies remain unaffected by variation of acceleration due to gravity.Q.3. A piece of ice is floating in a vessel containing water and inside the ice there is an air bubble. What will be the effect on the level of water, when the ice melts?
Answer
Answer: The level of water will not change because for a floating ice, the weight of ice is equal to the weight of the displaced water by the immersed part of ice. When the ice melts, the water so formed will be equal in volume which was displaced by the immersed part of the ice.Q.4. A body is just floating in a liquid whose density is equal to that of the body. What will happen to the body if it is slightly pressed and released?
Answer
Answer: The body will sink to the bottom.Q.5. Why is the water reservoir of a dam thicker at the bottom?
Answer
Answer: Because the pressure of water increases with increase in depth.Q.6. What is the value of surface tension of a liquid at critical temperature?
Answer
Answer: ZeroQ.7. When a liquid drop splits into large number of small drops, what is the change in the potential energy of small drops and the potential energy of the bigger drop?
Answer
Answer: Change is positive as on splitting the surface area increases and hence the work done to increase the surface area is stored as potential energy of small drops. So P.E. increases.Q.8. What will be the effect on the angle of contact of a liquid if the temperature increases?
Answer
Answer: Surface tension of liquid decreases with increase in temperature. So, the curvature of the meniscus decreases and the angle of contact increases.Q.9. Surface tension of lubricating oils and paints is generally low. Why?
Answer
Answer: So that it can spread over a large area.Q.10. The terminal velocity of a sphere of radius r in a viscous liquid is V. What is the terminal velocity of a sphere of radius 2r and of the same density in a given viscous fluid?
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Answer:
Q.11. An incompressible fluid flows steadily through a cylindrical pipe which has radius 2R at point A and radius R at point B, along the flow direction. If the velocity of liquid flow at A is v, what will be its velocity at B?
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Answer:
Q.12. Two liquids of densities d1 and d2 and coefficient of viscosities h1 and h2 are found to flow through a capillary tube at the same rate. Find the ratio of η1 and η2 ?
Answer
Answer:
Q.13. A hotter liquid flows faster than a colder one. Explain.
Answer
Answer: As the temperature of the liquid increases, its coefficient of viscosity will decrease. So the flow of liquid increases.Q.14. One flask containing glycerine and other water is shaken vigorously and then kept on a table. Which liquid will come to rest first?
Answer
Answer: Glycerine will come to rest earlier as its viscosity is larger than water, so the relative motion will be destroyed early in glycerine.Q.15. If instead of fresh water, sea water is filled in the tank, will the velocity of efflux will change?
Answer
Answer: No, because it is independent of the density of the liquid.Q.16. An egg when placed in ordinary water sinks but floats when placed in brine. Why? [HOTS]
Answer
Answer: The density of brine is greater than that of ordinary water. Due to its high density brine exerts an upthrust which can balance the weight of the egg.Q.17. How is an airplane able to fly upside down? [HOTS]
Answer
Answer: An airplane is able to fly upside down by using Bernoulli’s principle. When it turns upside down, the air pressure below the wings of the plane is more than that above it which keeps the plane floating.Q.18. A barge filled with scrap iron in a canal lock. If the iron is thrown overboard, does the water level at the side of the lock rise, fall, or remain unchanged? Explain. [HOTS]
Answer
Answer: When the iron is thrown overboard, then the mass of the barge will decrease, so its weight (acting downwards) will decreases. But the buoyant force remains the same. Now upward force becomes more than the downward force so the water level will rise.Q.19. How does the volume of a completely submerged object compare with the volume of water displaced? [HOTS]
Answer
Answer: When an object is completely submerged in water it displaces some water. The volume of the displaced water is equal to the volume of the object.Q.20. Is surface tension a vector? [Exemplar]
Answer
Answer: NoQ.21. Iceberg floats in water with part of it submerged. What is the fraction of the volume of iceberg submerged if the density of ice is ρi = 0.917 g cm–3?
Answer
Answer: Let the volume of the iceberg be V. The weight of the iceberg is ρiVg. If x is the fraction submerged, then the volume of water displaced is xV. The buoyant force is ρwxVg where ρw is the density of water.ρiVg = ρwxVg
x = ρi ⁄ρw = 0.917