28 + Interview Questions in FLUIDS-AT-REST IN GENERAL AWARENESS Page 1 InterviewSolution

1.	A thin wire is bent in the form of a ring of diameter 3.0 cm . The ring is placed horizontally on the surface of soap solution and then raised up slowly . How much upward force is necessary to break the vertical film formed between the ring and the solution ? surface tension of a soap solution `=3.0 xx 10^(-2) "Nm"^(-1).`
Answer» Correct Answer - `(5.65 xx 10^(-3)N)`

Discussion

2.	A rectangular plate of dimensions `6cm xx 4 cm` and thickness 2 mm is placed with its largest face flat on surface of water . (i) What is the downward force on the plate due to surface tension ? Surface tension of water `=7.0 xx10^(-2) "Nm"^(-1)` (ii) If the plate is placed vertical so that the longest side just touches the water surface, find the downward force on the plate.
Answer» Correct Answer - `(1.4xx10^(-2)N,8.68xx10^(-3)N)`

Discussion

3.	Calculate the amount force required to take away a flat plate of radius 5 cm from the surface of water . Given surface tension of water `= 72 "dyne"" "cm^(-1).`
Answer» Correct Answer - `(2260.8 dyne)`

Discussion

4.	A cubical block of wood 10 cm on a side floats at the interface between oil and water with its lower surface horizontal and 4 cm below the interface. The density of oil is `0.6 gcm^(-3)`. The mass of block is
Answer» Correct Answer - `(760 g)`

Discussion

5.	A force of `40 N` is applied on a nail , whose tip has an area of cross-section of `0.001 "cm"^(2).` Calculate the pressure on the tip.
Answer» Correct Answer - `(4xx10^(8) Nm^(2))`

Discussion

6.	The radius of capillary tube is 0.025 mm. If is held vetically in a liquid whose density is `0.8 xx 10^(3) "kg" m^(-3),` surface tension is `3.0xx10^(-2)"Nm"^(-1)` and for which the cosine of the angle of contact is 0.3. Determine the height upto which the liquid will rise in the tube . Given `g=10"ms"^(-2).`
Answer» Correct Answer - `(9cm)`

Discussion

7.	A piece of ice floats in water . What fraction of its volume will be above the surface of water ? Given density of ice `=0.90 xx10^(3)"kgm"^(-3).`
Answer» Correct Answer - `(0.10)`

Discussion

8.	The surface area of a soap-bubble is `2.0xx10^(-3) m^(2).` How much work will be done in blowing the bubble twice its surface area? Surface tension of soap solution `=3.0 xx 10^(-2) "Nm"^(-2).`
Answer» Correct Answer - `(1.2xx10^(-4)J)`

Discussion

9.	The diameter of a capillary tube is `0.4 xx 10^(-3)m`. It is held vertically in a liquid whose density is `0.8 xx 10^(3) "kgm"^(-3)` and the surface tension is `9.8 xx 10^(-2) "Nm"^(-1)`. Determine the height to which the liquid will rise in the tube. Given`g=9.8 "ms"^(-2)` and angle of contact is zero.
Answer» Correct Answer - `(12.5 cm)`

Discussion

10.	A soap bubble of radius `1//sqrtpi "cm"` is expanded to radius `2//sqrtpi "cm".` Calculate the work done. Surface tension of soap solution `=30 "dyne"" "cm^(-1).`
Answer» Correct Answer - `(720 erg)`

Discussion

11.	There is an air bubble of radius `1.0 mm ` in a liquid of surface tension `0.075"Nm"^(-1)` and density `10^(3) "kgm"^(-3)`. The bubble is at a depth of `10.0 cm` below the free surface of a liquid. By what amount is the pressure inside the bubble greater than the atmospheric pressure?
Answer» Correct Answer - `(1130 Nm^(-2))`

Discussion

12.	What is the difference in pressure between the inside and outside of a spherical drop of radius 2mm Surface tension of water `=70 xx 10^(-3) "Nm"^(-1).`
Answer» Correct Answer - `(70 Nm^(-2))`

Discussion

13.	A soap film is formed on a rectangular frame of length 7 cm dipping in soap solution. The frame hanges from the arm of a balance. An extra weight of 0.38 g is to be placed in the opposite pan to balance the pull on the frame. Calculate the surface tension of the soap solution. `"Given" g= 980 "cms"^(-2).`
Answer» Correct Answer - `(26.6"dyne" cm^(-1))`

Discussion

14.	A solid weighs `10 N` in air. Its weight decreases by `2 N` when weighed in water what is the density of solid?
Answer» Correct Answer - `(5000"kgm"^(-3))`

Discussion

15.	A piece of cork whose weight is 19 g is attached to a bar of silver weighing 63 g . The two together just float in water . Specific gravity of silver is `10.5.` Find the specitic gravity of cork. Density of water `=1 g "cm"^(-3).`
Answer» Correct Answer - `(0.25)`

Discussion

16.	How much will a body of `70 N ` weight in water if it displaces 20 ml of water ?
Answer» Correct Answer - `(68.04 N)`

Discussion

17.	A vertical U-tube of uniform inner cross-section contains mercury in both of its arms. A glycerine `("density" 1.3 "gcm"^(-3))` column of length `10 cm `is introduced into one of the arms Oil of density `0.8 "gcm"^(-3)` is poured in the other arm until the upper surface of the oil and glycerine are in the same horizontal level. Find the length of the oil column.
Answer» Correct Answer - `(9.6 "cm")`

Discussion

18.	A barometer kept in an elevator accelerating upwards reads 76 cm of Hg. If the elevator is accelerating upwards at `4.9 "ms"^(-2)` , what will be the air pressure in the elevator?
Answer» Correct Answer - `(114 cm "of Hg")`

Discussion

19.	The force on a Phonograph needle is `1.2 N.` the point has a circular cross-section whose radius is 0.1 mm. Find the pressure (in atm) it exerts on the recods. Given `1 "atm" = 1.013 xx 10^(5) Pa.`
Answer» Correct Answer - `(377 "atm")`

Discussion

20.	The area of cross-section of the wider tube shown in fig., is `800cm^(2)` . If a mass of 12 kg is placed on the massless piston, what is the difference in the level of water in two tubes.
Answer» Correct Answer - `(15.0 cm)`

Discussion

21.	A cylinderical vessel contaning liquid is closed by a smooth piston of mass m. the area of cross-section of the piston is A. if the atmospheric pressure is `P_(0),` Find the pressure of the liquid just below the piston.
Answer» Correct Answer - `(P_(0) + "mg"//A)`

Discussion

22.	In a hydraulic press used for compressing cotton the area of the piston is `0.1 m^(2)` and the force exerted along the piston rod is `200 N`. If the area of the larger cylinder is `0.8 m^(2)`, find the pressure produced in the cylinder and the total crushing force exerted on the bale of cotton.
Answer» Correct Answer - `(1600N,1280 Nm^(-2))`

Discussion

23.	The cross-section of two piston in hydraulic press are `2cm^(2) "and" 150 cm^(2)` respectivley . Calculate the minimum force required to support a weight of `2000"kg"` wt on the broader face of the press.
Answer» Correct Answer - `(261.3N)`

Discussion

24.	The average mass that must be lifted by a hydraulic press is `80 "kg"`.If the radius of the larger piston is five times that of the smaller piston, what is the minimum force that must be applied?
Answer» Correct Answer - `(31.4 N)`

Discussion

25.	Water rises in a capillary upto a height of 8.0 cm. if the capillary is inclined at an angle of `45^(@)` with the vertical then determine the vertical height of water. How much length of the capillary will be occupied by water ? If the length of the capillary is reduced to 4.0 cm and it is held vertically in water then what will be the position of water?
Answer» Correct Answer - `(8.0cm ,11.3 cm, "water will rese to the top of the tube but will rise to the tube")`

Discussion

26.	A glass tube of radius `0.4mm` is dipped vertically in water. Find upto what height the water will rise in the capollary? If the tube in inclined at an angle of `60^(@)` with the vertical, how much length of the capillary is occupied by water? Suface of water`=7.0xx10^(-2)N//m`,density of water `=10^(3)kg//m^(3)`.
Answer» Correct Answer - `(3.57 cm, 7.14 cm)`

Discussion

27.	The tube of mercury barometer is 4mm in diameter. How much error does the surface tension cause in the reading? Surface tension of mercury = `540" x "10^(-3) Nm^(-1)`, angle of contact = `135^(@)`. Density of mercury `= 13.6 xx 10^(3)kg m^(-3)`.
Answer» Correct Answer - `(0.2293 xx10^(-2)m)`

Discussion

28.	Two mercury drops each of radius r merge to form a bigger drop. Calculate the surface energy released.
Answer» Correct Answer - `(1.65 pir^(2)sigma)`

Discussion

Explore topic-wise InterviewSolutions in .

Calculate the amount force required to take away a flat plate of radius 5 cm from the surface of water . Given surface tension of water `= 72 "dyne"" "cm^(-1).`

A cubical block of wood 10 cm on a side floats at the interface between oil and water with its lower surface horizontal and 4 cm below the interface. The density of oil is `0.6 gcm^(-3)`. The mass of block is

A force of `40 N` is applied on a nail , whose tip has an area of cross-section of `0.001 "cm"^(2).` Calculate the pressure on the tip.

A piece of ice floats in water . What fraction of its volume will be above the surface of water ? Given density of ice `=0.90 xx10^(3)"kgm"^(-3).`

The surface area of a soap-bubble is `2.0xx10^(-3) m^(2).` How much work will be done in blowing the bubble twice its surface area? Surface tension of soap solution `=3.0 xx 10^(-2) "Nm"^(-2).`

A soap bubble of radius `1//sqrtpi "cm"` is expanded to radius `2//sqrtpi "cm".` Calculate the work done. Surface tension of soap solution `=30 "dyne"" "cm^(-1).`

There is an air bubble of radius `1.0 mm ` in a liquid of surface tension `0.075"Nm"^(-1)` and density `10^(3) "kgm"^(-3)`. The bubble is at a depth of `10.0 cm` below the free surface of a liquid. By what amount is the pressure inside the bubble greater than the atmospheric pressure?

What is the difference in pressure between the inside and outside of a spherical drop of radius 2mm Surface tension of water `=70 xx 10^(-3) "Nm"^(-1).`

A solid weighs `10 N` in air. Its weight decreases by `2 N` when weighed in water what is the density of solid?

A piece of cork whose weight is 19 g is attached to a bar of silver weighing 63 g . The two together just float in water . Specific gravity of silver is `10.5.` Find the specitic gravity of cork. Density of water `=1 g "cm"^(-3).`

How much will a body of `70 N ` weight in water if it displaces 20 ml of water ?

A barometer kept in an elevator accelerating upwards reads 76 cm of Hg. If the elevator is accelerating upwards at `4.9 "ms"^(-2)` , what will be the air pressure in the elevator?

The force on a Phonograph needle is `1.2 N.` the point has a circular cross-section whose radius is 0.1 mm. Find the pressure (in atm) it exerts on the recods. Given `1 "atm" = 1.013 xx 10^(5) Pa.`

The area of cross-section of the wider tube shown in fig., is `800cm^(2)` . If a mass of 12 kg is placed on the massless piston, what is the difference in the level of water in two tubes.

A cylinderical vessel contaning liquid is closed by a smooth piston of mass m. the area of cross-section of the piston is A. if the atmospheric pressure is `P_(0),` Find the pressure of the liquid just below the piston.

In a hydraulic press used for compressing cotton the area of the piston is `0.1 m^(2)` and the force exerted along the piston rod is `200 N`. If the area of the larger cylinder is `0.8 m^(2)`, find the pressure produced in the cylinder and the total crushing force exerted on the bale of cotton.

The cross-section of two piston in hydraulic press are `2cm^(2) "and" 150 cm^(2)` respectivley . Calculate the minimum force required to support a weight of `2000"kg"` wt on the broader face of the press.

The average mass that must be lifted by a hydraulic press is `80 "kg"`.If the radius of the larger piston is five times that of the smaller piston, what is the minimum force that must be applied?

The tube of mercury barometer is 4mm in diameter. How much error does the surface tension cause in the reading? Surface tension of mercury = `540" x "10^(-3) Nm^(-1)`, angle of contact = `135^(@)`. Density of mercury `= 13.6 xx 10^(3)kg m^(-3)`.

Two mercury drops each of radius r merge to form a bigger drop. Calculate the surface energy released.