# Multiple choice question for engineering

## Set 1

1. If the atmospheric pressure at sea level is 7.5 N/cm2, determine the pressure at a height of 3000m assuming the pressure variation follows isothermal law. The density of air is given as 1.2 km/m3.

a) 4.68 N/cm^{2}

b) 9.37 N/cm^{2}

c) 2.34 N/cm^{2}

d) None of the mentioned

### View Answer

^{-gZ/RT}=75000*e

^{ -9.81*3000*1.2/75000 }= 4.68 N/cm

^{2}.

2. The barometric pressure at sea level is 760 mm of Mercury while that on a mountain top is 715 mm. If the density of air is assumed constant at 1.2 kg/m^{3} , what is the elevation of the mountain top?

a) 510 m

b) 1020 m

c) 255 m

d) 128 m

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3. Calculate the pressure at a height of 6500m above the sea level if the atmospheric pressure is 10.145 N/cm2 and temperature is 25℃ assuming air is incompressible. Take density of air as 1.2 kg/m3. Neglect variation of g.

a) 4.98 N/cm^{2}

b) 2.49 N/cm^{2}

c) 1.24 N/cm^{2}

d) None of the mentioned

### View Answer

^{2}.

4. Calculate the pressure of air at a height of 3500m from sea level where pressure and temperature of air are 10 N/cm^{2} and 25℃ respectively. The temperature lapse rate is given as 0.0065 ℃ /m. Take density of air at sea level equal to 1.2 kg/m^{3}.

a) 19.7 N/cm^{2}

b) 9.85 N/cm^{2}

c) 4.93 N/cm^{2}

d) 6.24 N/cm^{2}

### View Answer

^{k/(k-1)}=9.85 N/cm

^{2}

Here, Lapse rate= -g/R*(k/k-1).

5. Pressure variation for compressible fluid is maximum for which kind of process?

a) Isothermal

b) Adiabatic

c) Quasi Static

d) None of the mentioned

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6. Why can’t the density be assumed as constant for compressible fluids?

a) It shows variation with temperature and pressure

b) It remains constant with temperature and pressure

c) It becomes almost constant at very high temperature

d) None of the mentioned

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7.What is the variation observed in temperature in atmosphere with respect to elevation?

a) It goes on decreasing with height

b) It goes on increasing with height

c) It first increases then decreases

d) It first decreases then increases

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8. As we go upwards, at height there is slight decrease in pressure variation.

a) True

b) False

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9. For dynamic fluid motion in a pipe, the pressure measurement cannot be carried out accurately by manometer.

a) True

b) False

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10. A simple U tube manometer connected to a pipe in which liquid is flowing with uniform speed will give which kind of pressure?

a) Absolute Pressure

b) Vacuum Pressure

c) Gauge Pressure

d) None of the mentioned

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## Set 2

1. Does total pressure takes into the account force exerted by the fluid when it is in the dynamic motion?

a) Yes

b) No

c) Depends on the conditions

d) Depends on the type of Motion

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2. Can centre of pressure for a vertical plane submerged surface be ever be above centre of Gravity

a) Yes

b) No

c) It can be above in cases where the surface height is very large

d) None of the mentioned

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3. Which principle is used for calculating the centre of pressure?

a) Principle of momentum

b) Principle of conservation of energy

c) Principle of balancing of momentum

d) None of the mentioned

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4. In a vertically submerged plane surface, pressure at evbery point remains same

a) True

b) False

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5. The magnitude of total pressure and centre of pressure is independent on the shape of the submerged plane surface.

a) True

b) False

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6. What is the variation of total pressure with depth for any submerged surface if we neglect variation in the density?

a) Linear

b) Parabolic

c) Curvilinear

d) Logarithmic

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7. A pipe line which is 6 m in diameter contains a gate valve. The pressure at the centre of the pipe is 25 N/cm2. If the pipe is filled with specific gravity 0.8, find the force exerted by the oil upon the gate.

a) 7.06 MN

b) 14.12 MN

c) 3.53 MN

d) 28.24 MN

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8. Determine the centre of pressure on an isosceles triangle plate of base 6m and altitude 6m when it is immersed vertically in an oil of specific gravity 0.75. The base of the plate coincides with the free surface of oil.

a) 6 m

b) 3 m

c) 9 m

d) 12 m

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9. A tank contains water upto a height of 0.5 m above the base. An immiscible liquid of specific gravity 0.75 is filled on the top of water upto 1.5 m height. Calculate total pressure on side of the tank.

a) 17780.61 N/m2

b) 35561.22 N/m2

c) 71122.44 N/m2

d) 8890.31 N/m2

### View Answer

^{2}.

10. A circular opening, 6m diameter, in a vertical side of a tank is closed by a disc of 6m diameter which can rotate about a horizontal diameter. Calculate the force on the disc. The centre of circular opening is at the depth of 5 m.

a) 1.38 MN

b) 2.76 MN

c) 5.54 MN

d) 7.85 MN

### View Answer

^{2}*5 =1.38 MN.

## Set 3

1. Which of the following contribute to the reason behind the origin of surface tension?

a) only cohesive forces

b) only adhesive forces

c) neither cohesive forces nor adhesive forces

d) both cohesive forces and adhesive forces

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2. A soap film is trapped between a frame and a wire of length 10 cm as shown.

If the surface tension is given as 0.0049 N/m, what will be the value of m (in mg) such that the wire remains in equilibrium?

a) 0.1

b) 1

c) 10

d) 100

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3. What will be the diameter (in mm) of a water droplet, the pressure inside which is 0.05 N/cm^{2} greater than the outside pressure? (Take surface tension as 0.075 N/m)

a) 3

b) 0.3

c) 0.6

d) 6

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4. A soap bubble of d mm diameter is observed inside a bucket of water. If the pressure inside the bubble is 0.075 N/cm^{2}, what will be the value of d? (Take surface tension as 0.075 N/m)

a) 0.4

b) 0.8

c) 1.6

d) 4

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5. A liquid jet of 5 cm diameter has a pressure difference of N/m^{2}. (Take surface tension as 0.075 N/m)

a) 12

b) 6

c) 3

d) 1.5

### View Answer

^{-2}= 1.5 N/m

^{2}.

6. The rise in the level of a liquid in a tube is h. What will be the rise in the level if the same amount of liquid is poured into a tube of half the diameter.

a) 0

b) h/2

c) h

d) 2h

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7. The ratio of the surface tension S and density ρ of liquid 1 and 2 are 1:2 and 1:4 respectively. Equal amount of the two liquids is poured into two identical tubes. what will be the ratio of the rise in the liquid level in the two tubes? (Assume the angle of contact to be same)

a) 1:2

b) 2:1

c) 8:1

d) 1:8

### View Answer

_{1}/ ρ

_{1}= 1 : 2 and S

_{2}/ ρ

_{2}= 1 : 4.

8. The rise in the level of a liquid in a tube is h. If half the amount is poured outside, what will be the new rise in liquid level?

a) 0

b) h/2

c) h

d) 2h

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9. If a glass tube of 10 mm diameter is immersed in water, what will be the rise or fall in capillary?

(Take surface tension = 0.075 N/m, g = 10 m/s^{2} and angle of contact = 0)

a) 0.75

b) 1.5

c) 3

d) 6

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10. A water drop of diameter 1 cm breaks into 1000 similar droplets of same diameter. What will be the gain or loss in the surface energy? (Take surface tension as 0.075 N/m)

a) gain of 0.424 mJ

b) gain of 0.212 mJ

c) loss of 0.212 mJ

d) loss of 0.424 mJ

### View Answer

^{3}= 1000 * d

^{3}, i.e. D = 10d, where D = diameter of big drop, d = diameter of a droplet. Change in surface energy = Surface tension * Change in surface area = 0:075*(1000 * πd

^{2}– πD

^{2}) = 0:075 * (10 * πD

^{2}– πD

^{2}) = 0:075 * 9π * (10-2)

^{2}= 0:212 mJ Since, the change is positive, there will be a gain in the surface energy.

## Set 4

1. Calculate the magnitude of capillary effect in millimeters in a glass tube of 7mm diameter, when immersed in mercury. The temperature of the liquid is 25℃ and the values of surface tension of mercury at 25℃ is 0.51 N/m. The angle of contact for mercury is 130°.

a) 140

b) 280

c) 170

d) 210

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2. Determine the minimum size of glass tube that can be used to measure water level if the capillary rise in the tube is restricted to 5mm. Consider surface tension of water in contact with air as 0.073 N/m

a) 5.95mm

b) 11.9mm

c) 2.97mm

d) 4.46mm

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3. An oil of vicosity 7 poise is used for lubrication between shaft and sleeve. The diameter of shaft is 0.6 m and it rotates is 360 rpm. Calculate the power lost in oil for a sleeve length of 160mm. The thickness of oil film is 1.0mm

a) 25.31 kW

b) 50.62 kW

c) 37.97 kW

d) 12.65 kW

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4. Find the capillarity rise or fall if a capillary tube of diameter .03m is immersed in hypothetical fluid with specific gravity 6.5, surface tension 0.25 N/m and angle of contact 147°.

a) 0.44mm fall

b) 0.88mm fall

c) 0.44mm rise

d) 0.88mm rise

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5. Will capillary rise occur and if it occurs what will be capillary rise if glass capillarity tube is immersed in water and experiment is carried out by astronauts in space.

a) Capillarity rise will not occur

b) Capillarity rise will occur infinitely and will come out in form of fountain

c) Capillarity rise will occur finitely and will be the whole length of tube

d) None of the mentioned

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6. The surface tension of fluid in contact with air at 25℃ is 0.51N/m. The pressure inside a droplet is to be 0.05 N/cm2 greater than outside pressure. Determine the diameter of the droplet of water.

a) 4.08mm

b) 8.16mm

c) 2.04mm

d) None of the mentioned

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7. If a fluid of certain surface tension and diameter is used to create a soap bubble and a liquid jet. Which of the two, bubble or liquid jet, will have greater pressure difference on the inside and outside.

a) Liquid jet

b) Soap bubble

c) Both will have same pressure differrence

d) None of the mentioned

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8. Capillarity fall is reduced if we take the appartus (capillary tube immersed in fluid having acute angle of contact) considerable distance inside the earth( i.e below the earth crust).

a) True

b) False

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9. For liquid fluids will capillarity rise (or fall) increase or decrease with rise in temperature.

a) Increase

b) Decrease

c) Remain constant

d) First decrease then increase

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10. Cavitation is more pronounced in rough pipes than smooth surfaced pipes.

a) True

b) False

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## Set 5

1. The greatest and the least depth of a circular plate of 4 m diameter from the free surface of water are 3m and 1 m respectively as shown. What will be the total pressure in (kN) on the plate?

a) 123

b) 185

c) 246

d) 308

### View Answer

^{3}N / m

^{3}; y = 1 + 3 – 1 / 2 – 2m, A =

^{π}⁄

_{4}* 4

^{2}= 4π m

^{2}. Hence, F = 246.55 kN.

2. The greatest and the least depth of a circular plate of 4 m diameter from the free surface of water are 3m and 1 m respectively as shown. What will be the depth (in m) of it’s centre of pressure?

a) 1.125

b) 1.25

c) 2.125

d) 2.25

### View Answer

_{CP}are related by: where I= the moment of inertia and A = area and θ = the angle of inclination of the lamina to the horizontal. Now, y = 1 + 3 – 1 / 2 = 2, I =

^{π}⁄

_{64}* 4

^{2}= 4π, A =

^{π}⁄

_{4}* 4

^{2}= 4π, sin θ =

^{1}⁄

_{2}Thus, y

_{CP}= 2.125m.

3. The highest and lowest vertices of a diagonal of a square lamina (each side equal to 4m) are 1 m and 3 m respectively as shown. What will be the water force (in kN) on the lamina?

a) 78

b) 118

c) 157

d) 196

### View Answer

^{3}N / m

^{3}; y = 1 + 3 – 1 / 2 = 2m, each side of the lamina = Hence, F = 156:96 kN.

4. The highest and lowest vertices of a diagonal of a square lamina (each side equal to 4m) are 1 m and 3 m respectively as shown. What will be the depth (in m) of it’s centre of pressure?

a) 1.08

b) 1.58

c) 2.08

d) 2.58

### View Answer

^{ 1}⁄

_{2}. Thus, y

_{CP}= 2.08m.

5. A square lamina (each side equal to 2m) is submerged vertically in water such that the upper edge of the lamina is at a depth of 0.5 m from the water surface. If the pressure on the surface is 12 bar, what will be the total water pressure (in kN) on the lamina?

a) 39

b) 59

c) 64

d) 71

### View Answer

^{3}N / m

^{3}; A = 2 * 2 = 4 m

^{2}. Hence, F = 63.65 kN.

6. A container is filled with two liquids of densities ρ1 and ρ2 up to heights h_{1} and h_{2} respectively. What will be the hydrostatic force (in kN) per unit width of the lower face AB?

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7. A container is filled with two liquids of densities ρ and 2ρ up to heights h and eh respectively. What will be the ratio of the total pressure on the lower face AB and on the upper face BC?

a) 1 : 1

b) 3 : 1

c) 2 : 1

d) 3 : 2

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8. A container is filled with two liquids of densities ρ and 2ρ up to heights h and eh respectively. What will be the ratio of the depths of the centres of pressure of the upper face BC and the lower face AB?

a) 1 : 2

b) 3 : 4

c) 2 : 3

d) 3 : 2

### View Answer

9. A gate of length 5 m is hinged at A as shown to support a water column of height 2.5 m. What should be the minimum mass per unit width of the gate to keep it closed?

a) 3608

b) 4811

c) 7217

d) 9622

### View Answer

_{hyd}= hydrostatic force on the plate, x = distance of the point of action of F

_{hyd}from the hinge point =

^{2}⁄

_{3}* 5 =

^{10}⁄

_{3}F

_{hyd}= γyA, where γ = specific weight of the liquid = 9.81 * 10

^{3}y = depth of the centre of pressure from the free surface = 2.5/2 = 1.25 and A = 5 * 1. Substituting all the values in the equation, we get m = 9622.5g.

10. A large tank is filled with three liquids of densities ρ1, ρ2 and ρ3 up to heights of h_{1}, h_{2} and h_{3} respectively. What will be the expression for the instantaneous velocity of discharge through a small opening at the base of the tank? (assume that the diameter of the opening is negligible compared to the height of the liquid column)

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11. A large tank of height h is filled with a liquid of density ρ. A similar tank is half-filled with this liquid and other-halffilled with another liquid of density 2ρ as shown. What will be the ratio of the instantaneous velocities of discharge through a small opening at the base of the tanks? (assume that the diameter of the opening is negligible compared to the height of the liquid column in either of the tanks)

a) 2 : 3

b) 2 : √3

c) √2 : 3

d) √2 : √3

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12. A large tank of height h is half-filled with a liquid of density ρ and other half-filled with a liquid of density 4ρ. A similar tank is half-filled with a liquid of density 2ρ and other-half filled with another liquid of density 3ρ as shown. What will be the ratio of the instantaneous velocities of discharge through a small opening at the base of the tanks? (assume that the diameter of the opening is negligible compared to the height of the liquid column in either of the tanks)

a) 1 : 1

b) 1 : 2

c) 2 : 1

d) 1 : 3

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13. A large tank is filled with three liquids of densities ρ, 2ρ and 3ρ up to a height of ^{h} ⁄ _{3} each. What will be the expression for the instantaneous velocity of discharge through a small opening at the base of the tank? (assume that the diameter of the opening is negligible compared to the height of the liquid column)

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14. A large tank is filled with three liquids of densities ρ, 2ρ and 3ρ up to heights of ^{h} ⁄ _{6}, ^{h} ⁄ _{3} and ^{h} ⁄ _{2} respectively. What will be the ratio of the instantaneous velocity of discharge through a small opening at the base of the tank in this case to that if the container is filled with the liquid of density ρ only? (assume that the diameter of the opening is negligible compared to the height of the liquid column)