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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A body of mass 2.0 kg and density 8000 `(kg)/(m^3)` is completely dipped in a liquid of density 800 `(kg)/(m^3)`. Find the force of buoyancy on it. |
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Answer» Here, mass of the body in air, `M=2.0kg` density of the body, `d=9000(kg)/(m^3)` Density of the liquid, `d_l=800(kg)/(m^3)` volume of the body, `V=(M)/(d)=(2.0kg)/(8000(kg)/(m^3))` Volume of liquid displaced when the body is completely dipped in it `=` volume of the body `=2.5xx10^-4m^3` mass of the liquid displaced, `m=Vd_l=(2.5xx10^-4m^3)(800(kg)/(m^3))=0.2kg` weight of the liquid displaced, `W_l=mg=(0.2kg)(10(m)/(s^2))=2N` Force of buoyancy, `F_B=W_l=2N` |
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| 2. |
(a) What is 1 atm? (b) What is the relation between 1 atm and pascal? |
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Answer» (a) It is the unit of measurement of pressure and 1 atm`=760mm` of Hg column. (b) 1 atm`=1.013xx10^5Pa` |
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| 3. |
what is 1 pascal? |
| Answer» 1 pascal `(Pa)=1(N)/(m^2)` | |
| 4. |
In his original barometer, Pascal used water instead of mercury. Water is lwss dense than mercury, so the water barometer would have:(a) higher height than, (b) a lower height than, or (c ) the same height as the mercury barometer. Why? |
| Answer» (a) higher height than the mercury barometer due to lower density of water as compared to that of mercury. | |
| 5. |
(a) Gallinule (an aquatic bird with exceptionally long toes that are spread out over a large area) can actually walk across lily pads without sinking. Explain. (b) One day while ewimming below the surface of the ocean, you let out a small bubble of air from your mouth. What happens to the bubble as it rises towards the surface? |
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Answer» (a) The bird exerts only a small pressure on the lily pads on which it walks because its weight is spred out over a large area by its long toes. Since the pressure is not enough to sink the lily pads, the bird can actually walk across the lily bads without sinking into water i.e., the bird can seemingly ``walks on water`` (b) As the bubble rises the pressure in the surrounding water decreases (as `P=hrhog` and with decreasing depth h,P decreases). This allows the air in the bubble to expand and occupy a larger volume (i.e., the diameter of the bubble increases). |
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| 6. |
Why do you feel lighter when you swim? |
| Answer» A person weighs less in water than in air due to buoyancy acting on him and as such he feels lighter. | |
| 7. |
Why is it easier to walk on soft sand with a flat shoe than with a pencil-heeled shoe? |
| Answer» A flat shoe has a larger area in contact with the sand and as such exerts less pressure on it. On the other hand, A pencil-heeled shoe exerts more pressure on the ground as it has smaller area in contact with sand. Thus, a flat shoe does not sink into sand whereas a pencil heeled shoe does. It is due to the similar reason that a camel can run easily in a desert. | |
| 8. |
Why is it easier to swim in sea water than in river water? |
| Answer» Sea water is heavier than river water (density of sea water is around `1040(kg)/(m^3)`). Thus the immersed portions of the body of a swimmer experience greater buoyancy in sea water than in river water. | |
| 9. |
A hydrometer floats with half of its stem outside water surface. It is now placed in alcohol `(RD=0.8)`. The hydrometer floats:A. with stem at the same positionB. with more stem inside the alcoholC. with more stem outside alcoholD. in tilted position. |
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Answer» Correct Answer - B The length of a hydrometer immersed is inversely proportional to the density of the liquid in which it is placed. |
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| 10. |
Salt water is slightly dense than fresh water. Will a boat float higher in salt water on in fresh water? |
| Answer» Higher in salt water. | |
| 11. |
An airplane window has an area of 825`cm^2`. Cabin pressure is 1 atm, and the outside pressure in 0.3 atm. Find the force produced by air pressure on the window. |
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Answer» `F=P_1A-P_2A` `=(P_1-P_2)A` `A=(1atm-0.3atm)(825cm^2)` `=(0.7)(1.01xx10^5(n)/(m^2))(825xx10^-4m^2)=5.83xx10^2N` |
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| 12. |
A dam for water reservoir is built whicker at the bottom than at the top because:A. pressure of water is very large at the bottom due to its large depthB. water is likely to have more density at the bottom due to its large depthC. quantity of water at the bottom is largeD. none of these |
| Answer» Correct Answer - A | |
| 13. |
When measuring automobile tyre pressure, what type of presure is this:A. gaugeB. absoluteC. relativeD. all of the precending |
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Answer» Correct Answer - A Gauge pressure `(P_g)` is the difference between the true pressure (i.e., absolute pressure, P) in the tyres and the atmospheric pressure `(P_0)` i.e.,`P_g=P-P_0` |
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| 14. |
A hydraulic automobile lift is designed to lift cars with a maximum mass of `3000Kg`. The area of cross section of the piston carrying the load is `425cm^(2)`. What maximum pressures would the smaller piston have to bear? |
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Answer» `A=425cm^2=425xx10^-4m^2`,`F=3000kgwt=3000kgwt=3000xx10N=30000N` pressure on the larger piston, `P=(F)/(A)=(30000N)/(425xx10^-4m^2)=705882Pa` Since the pressure is transmitted equally in all direction, pressure on the smaller piston is also 705882 Pa |
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| 15. |
Automobile tyres are inflated to about 30 `("pound")/("inch"^2)((lb)/("in"^2))` whereas bicycle tyres are inflated to 90 to `115(lb)/(I n^2), at leastthree times as much pressure ! Why? |
| Answer» Bicycle tyres have a much smaller contact area with ground so they need a high pressure to balance the weight of the bicycle and the rider. | |
| 16. |
Why is the pressure on the ground more when a man is walking than when he is standing? |
| Answer» When a man walks only one of his feet is on the ground. Due to this, the force of the weight of the man falls on a smaller area of the ground and the pressure on ground increases. On the other hans, when the man is standing, then both of his feet are on the ground and his weight now falls on a larger area of the ground. Thereby producing lesser pressure on the ground. | |
| 17. |
Find the thrust acting on the human body due to atmospheric pressure. Take the surface area of a man of middle size to be `1.5m^2` and atmospheric pressure (1 atm)`=1.013xx10^5` Pa. |
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Answer» Here, surface area of the human body, `A=1.5m^2` pressure acting on the body, `P=1.013xx10^5Pa=1.013xx10^5(N)/(m^2)` Thus, thrust acting on the human body, `F=PxxA=(1.013xx10^5(N)/(m^2))xx(1.5m^2)` `=1.52xx10^5N` `=1.52xx10^4kgwt=15.2tonwht` |
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| 18. |
(a) The density of a liquid is `860(kg)/(m^3)`. What will be its relative density? (b) The density of silver is 10500 `(kg)/(m^3)`. Explain this statement. |
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Answer» (a) 0.860. (b) The statement means that 1 `m^3` of silver has a mass of 10500 kg (or 1 `cm^3` of silver has a mass of 10.5 g). |
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| 19. |
When a plastic block is released under water, it never stays under water but instead comes to the suface of water. Explaing Why? |
| Answer» Whe buoyant force acting on the plastic block is greater than its weight as density of the block is less than that of water. The block comes to the surface of water due to net upward force acting on it. | |
| 20. |
The titanic was found in 1985 lying on the bottom of the north atlantic at a depth of 2.5 miles. What is the pressure at this depth? (Given 1 mile`=1609m1) |
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Answer» `P=P_0+rhogh=(1.01xx10^5Pa)+(1025(kg)/(m^3))(9.81(m)/(s^2))(2.5miles)((1690m)/(1"mile"))` `=4.1xx10^7Pa=400atm` ("as density of sea water " `rho=1025(kg)/(m^3)`) |
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| 21. |
Why does a load freighter sit lower in water than an empty one? |
| Answer» The loaded freighter must displace more water before the buoyant force is equal to its weight. | |
| 22. |
When a body is weighed in a liquid, the loss in its weight depends upon:A. volume of the bodyB. mass of the bodyC. shape of the bodyD. ventre of gravity of the body |
| Answer» Correct Answer - A | |
| 23. |
A device used to check the purity of milk is called:A. lactometerB. HydrometerC. speedometerD. barometer |
| Answer» Correct Answer - A | |
| 24. |
Two stretched membranes of areas `2cm^(2)` and `3cm^(2)` are placed in a liquid at the same depth. The ratio of the pressures on them is:A. `1:1`B. `2:3`C. `3:2`D. `2^(2):3^(2)` |
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Answer» Correct Answer - A Pressure is the same for a given depth. |
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| 25. |
Why is it difficult to hold a school bag having strap made of thin and strong string? |
| Answer» We know that pressure`=`force/area. When the string of the school bag is thin, its area is small and as such the pressure exerted on shoulders or the hands supporting the bag is large. In this case, the force acting on the shouldfers or the hand which support the bag is equal to the weight of the bag. In case the strap is broad (as is usually the case), the area on which the force (weight of the bag) acts in large and the pressure reduced (as the weight of the bag is now distributed over a larger area. | |
| 26. |
Define pressure. What is its unit? |
| Answer» Thrust per unit area is called pressure. The unit of pressure is called pascal (Pa). Where 1 Pa`=1(N)/(m^2)`. | |
| 27. |
Calculate the mass of air enclosed in a room of length, breadth and height equal to 5m, 3m and 4m respectively. Density of air `=1.3(kg)/(m^3)`. |
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Answer» `V=5mxx3mxx4m=60m^3` `d=1.3(kg)/(m^3)` `M=Vxxd=(60m^3)xx(1.3(kg)/(m^3))=78kg` |
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| 28. |
A tank with length 10 m, breadth 8 m and depth 6 m is filled with water upto top . If `G=10m//s^2`. And density of water `=1000kg//m^3`, then the thrust on the bottom is:A. `(6xx1000xx10xx80)`NB. `(3xx1000xx10xx48)` NC. `(3xx1000xx10xx60)` ND. `(3xx100xx10xx80)` N |
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Answer» Correct Answer - A Volume of water, `V=(10xx8xx6)(1000)(10)=(6xx1000xx10xx80)N` |
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| 29. |
Calculate the pressure when a force of 200 N acts on an area of (a) `10m^2` (b) `5m^2`. |
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Answer» (a) `P_1=(F_1)/(A_1)=(200N)/(10m^2)=20P` (b) `P_2=(F_2)/(A_2)=(200N)/(5m^2)=40Pa` |
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| 30. |
how much force should be applied on an area of 1 `cm^2` to get a pressure of 15 Pa? |
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Answer» Here, area, `A=1cm^2=10^-4m^2` pressure, `P=15Pa=15(N)/(m^2)` as `P=(F)/(A)`,`F=xxA=(15(N)/(m^2))xx(10^-4m^2)` `=1.5xx10^-3N` |
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| 31. |
The mass of a solid rectangular block of iron is 23.6g and its dimensions are `2.1cmxx1.2xx1.1cm`. Calculate the density of iron. |
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Answer» `V=2.1cmxx1.2cmxx1.1cm=2.772cm^3` `M=23.6g` `d=(M)/(V)=(23.6g)/(2.772cm^3)=8.514(g)/(cm^3)=8.514xx1000(kg)/(m^3)=8514(kg)/(m^3)` |
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| 32. |
A raft of wood (density`=600kg//m^(3))` of mass `120 kg` floats in water. How much weight can be put on the raft to make it just sink?A. 120 kgB. 200 kgC. 40 kgD. 80 kg |
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Answer» Correct Answer - D Volume of the raft`=(120kg)/(0.6xx10^3(kg)/(m^3))=200xx10^-3m^3` When the raft just sinks, Total weight of the raft (weight of the raft`+`weight put on the raft)`=`buoyancy of water `=(200xx10^-3m^3)(1000(kg)/(m^3))=200kgwt` Weight that can be put on the raft`=200kgwt-120kgwt=80kgwt` |
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| 33. |
A ship made of iron and steel does not sink in sea, but the same amount of iron and steel in form of a sheet would sink Why? |
| Answer» A ship has a larger volume as compared to the solid sheet of the same mass. Accordingly, a part of the ship displaces more water than the entire solid sheet and thus experiences more buoyant force and does not sink. One can argue like this also. The average density of an object`=` mass of the object/volume of the object. Since, the volume of the ship is much more than that of the solid sheet of the same mass, average density of ship is less than that of water. Hence, the ship floats. The sheet sinks as its average density is more than water. | |
| 34. |
Why are you more easily able to sink to the bottom of the swimming pool when you expel as much air as possible from your lungs? |
| Answer» Your average density increases with less air in your lungs. | |
| 35. |
A wooden block of dimensions `10cmxx20cmxx50cm` weighs 6-5 kg Calculate the density of the block. |
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Answer» Here, volume of the block, `V=10cmxx20cmxx50cm=10000cm^3` `=10000xx10^-6cm^3=10^-2m^3` mass of the block, `M=6.5kg` Density of the block, `d=(M)/(V)=(6.5kg)/(10^-2)=650(kg)/(m^3)` |
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| 36. |
In which unit is thrust measured? |
| Answer» The unit for measurement of thrust the same as that of force i.e., newton (N). | |
| 37. |
How is pressure related to thrust? |
| Answer» Pressure`=`(thrust)/(ar ea)` | |
| 38. |
What is borograph? |
| Answer» It is an instrument for automatically recording on a chart a countinuous variation of the atmospheric pressure. | |
| 39. |
Define density. Give its unit? |
| Answer» Density of a substance is its mass per unit volume. The unit of density is `(kg)/(m^3)`. | |
| 40. |
What is an altimeter? |
| Answer» An aneroid barometer provided with a scale to indicate height(attitude) is called an altimeter | |
| 41. |
What is relative density? What is its unit? |
| Answer» Relative density of a substance is defined as the ratio of its density to the density of water at `4^@C`. Since relative density is the ratio of two similar quantities, it has no unit. | |
| 42. |
What is weather glass? |
| Answer» the weather glass is a household barometer and is a form of siphon barometer. | |
| 43. |
Calculate the buoyant force on a helium filled balloon having a volume of 14000`cm^3`. |
| Answer» Buoyant force, `F_B=Vrhog=(14000xx10^-6)(1.20)(9.8)=0.165N` | |
| 44. |
Which one of the following would a hydrogen balloon find easiest to lift?A. one kg of steelB. one kg of lightly packed feathersC. one kg of waterD. all the same. |
| Answer» Correct Answer - B | |
| 45. |
A weather forecasting plastic balloon of volume `15m^3` contains hydrogen of density `0.09(kg)/(m^3`. The mass of the empty balloon is 7.15kg Calculate (a) the mass of hydrogen in the balloon (b) the mass of the balloon filled with hydrogen. |
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Answer» (a) mass of hydrogen, `M=Vxxd=(15m^3)(0.09(kg)/(m^3))=1.35kg` (b) mass of balloon filled with hydrogen`=1.35kg+7.15kg=8.50kg` |
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| 46. |
Find the pressuer exerted on the skin of a balloon with a force of 2.1 N usint (a) your finger of (b) a needle. Assume the area of your finger tip is `1.0xx10^-4m^2`, and the area of the needle tip is `2.5xx10^-7m^2`. (c ) Find the maximum force necessary to burst the balloon with the needle given that the balloon bursts with pressure of `3.0xx10^5(N)/(m^2)`. What insight you gain from the results obtained? |
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Answer» (a) ` P_(finger)=(F)/(A)=(2.1N)/(1.0xx10^-4m^2)=2.1xx10^-4(N)/(m^2)` (b) ` P_(needle)=(F)/(A)=(2.1N)/(2.5xx10^-7m^2)=8.4xx10^6(N)/(m^2)` (c ) `F=PA=(3.0xx10^5(N)/(m^2))(2.5xx10^-7m^2)=0.075N` Note that the pressure exerted by needle in part (b) is 400 times greater than the pressure due to finger in part (a). This increase in pressure with decreasing area accounts for the sharp tips to be found on such objects as nails, pens and pencils, and syringes. |
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| 47. |
The reading of a spring balance when a block is suspended from it in air is 60 N. This reading is changed to 40 N when the block is submerged in water. The relative density of the block is:A. 3B. 2C. 6D. `(3)/(2)` |
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Answer» Correct Answer - A Relative density`=(60N)/(60N-40N)=3` |
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| 48. |
(a) Which has greater denstiy: 1kg or iron or 2 kg of iron? (b) If a hollow sphere and a solid sphere are both made of the same amount of iron, which sphere has greater average density? |
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Answer» (a) They have the same density as the density of a material does not depend on the amount of material. (b) The solid sphere has the greater average density because it occupies the smallest volume for a given mass of iron. |
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| 49. |
(a)How could you use a borometer to measure the height of a mountain pass? (b) Why can water not be sucked to a height greater than 10 m even with a good suction pump? |
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Answer» (a) Air pressure decreases with height. A barometer used to measure height is called altimeter (where pressure is caliberated in terms of height). (b) It is the atmospheric pressure [76 cm of Hg column or `(76xx13.6)cm=10.3m` of water column] that determines the maximum height. |
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| 50. |
What is an aneroid borometer? |
| Answer» In this barometer provided with a scale to indicate geight (attitude) is called an altimeter. | |