# Multiple choice question for engineering

## Set 1

1. How many types of fluid flow are characterized in the realms of fluid mechanics?

a) 1

b) 2

c) 3

d) 4

### View Answer

2. In which fluid flow, the motion of fluid particles is irregular?

a) Turbulent

b) Laminar

c) One dimensional

d) Two dimensional

### View Answer

3. Following are the characteristics of turbulent flow

(i) Eddying

(ii) Sinuous

(iii) Rectilinear

Identify the correct option

a) 2 and 3

b) 1 and 3

c) 1, 2 and 3

d) 1 and 2

### View Answer

4. The nature of fluid flow is governed by following parameters

(i) Mean flow velocity

(ii) Density of fluid

(iii) Dynamic viscosity of the fluid

Identify the correct statements

a) 1 and 3

b) 1 only

c) 1, 2 and 3

d) 2 and 3

### View Answer

5. The value of convective coefficient of air in case of free convection is

a) 3-7 W/m^{2} K

b) 3-4 W/m^{2} K

c) 8-9 W/m^{2} K

d) 9-9.5 W/m^{2} K

### View Answer

^{2}K to 7 W/m

^{2}K. This is due to presence of some moisture in air.

6. The fluid particles move in flat or curved un-mixing layers or streams and follow a smooth continuous path. This type of flow is known as

a) Steady flow

b) Stream flow

c) Turbulent flow

d) Laminar flow

### View Answer

7. The characteristic dimension d in the relation R _{E }= V d p/δ is the equivalent diameter and is defined as how many times the cross-sectional flow area divided by wetted perimeter

a) 7

b) 4

c) 1

d) 6

### View Answer

8. For a duct of rectangular cross-section with length l and breadth b, the value of d _{e} is

a) l b / l + b

b) 2 l b

c) 2 l b / l + b

d) 4 l b / l + b

### View Answer

_{e}= 4 (l) (b)/2 l + 2 b.

9. In many flow situations, the duct can be

(i) Circular

(ii) Rectangle

(iii) Trapezoidal

(iv) Annulus

Identify the correct option

a) 1 and 2

b) 1, 2, 3 and 4

c) 1, 2 and 3

d) 3 and 4

### View Answer

10. If an annulus has an inner diameter of d_{ 1} and an outer diameter of d_{ 2} then the equivalent diameter is

a) 2 d_{ 2 }– d_{ 1}

b) d_{ 2 }– 2 d_{ 1}

c) d_{ 1 }– d_{ 2 }

d) d_{ 2 }– d_{ 1}

### View Answer

_{ 2}

^{2}

_{ }– d

_{ 1}

^{2})/π (d

_{ 1}+ d

_{ 2}).

## Set 2

1. Glycerin at 10 degree Celsius flows past a flat plate at 20 m/s. Workout the velocity components at a point P(x, y) in the fluid flow where

x = 2 m from the leading edge of the plate

y = 5 cm from the plate surface

For glycerin at 10 degree Celsius, kinematic viscosity = 2.79 * 10 ^{-3} m^{2}/s

a) 15.92 m/s and 0.0952 m/s

b) 16.92 m/s and 0.0952 m/s

c) 17.92 m/s and 0.0752 m/s

d) 18.92 m/s and 0.0752 m/s

### View Answer

_{INFINITY }= 0L.846 and v/U

_{INFINITY }(Re)

^{½}= 0.57.

2. A plate 0.3 m long is placed at zero angle of incidence in a stream of 15 degree Celsius water moving at 1 m/s. Find out the stream wise velocity component at the mid-point of the boundary layer. For water at 15 degree Celsius

p = 998.9 kg /m^{3}

µ = 415.85 * 10 ^{-2} kg/hr m

a) 0.736 m/s

b) 0.636 m/s

c) 0.536 m/s

d) 0.436 m/s

### View Answer

_{INFINITY}/v x)

^{½}= 2.5.

3. Air at 25 degree Celsius flows over a flat surface with a sharp leading edge at 1.5 m/s. Find the boundary layer thickness at 0.5 from the leading edge. For air at 25 degree Celsius, kinematic viscosity = 15.53* 10n ^{-6} m^{2}/s

a) 4.1376 cm

b) 3.1376 cm

c) 2.1376 cm

d) 1.1376 cm

### View Answer

^{½}= 1.1376 m.

4. Local skin friction coefficient is given by

a) 0.646/ (Re)^{ 1/2}

b) 1.646/ (Re)^{ 1/2}

c) 2.646/ (Re)^{ 1/2}

d) 3.646/ (Re)^{ 1/2}

### View Answer

^{ ½}.

5. A plate 0.3 m long is placed at zero angle of incidence in a stream of 15 degree Celsius water moving at 1 m/s. Find out the maximum boundary layer thickness. For water at 15 degree Celsius. For water at 15 degree Celsius

p = 998.9 kg /m^{3}

µ = 415.85 * 10 ^{-2} kg/hr m

a) 4.945 m

b) 3.945 m

c) 2.945 m

d) 1.945 m

### View Answer

_{INFINITY}/µ.

6. Shear stress at the middle of the plate is given by

a) T _{W} = 0.964 p U _{INFINITY }^{2}/2 (Re) ^{1/2}

b) T _{W} = 0.864 p U _{INFINITY }^{2}/2 (Re) ^{1/2}

c) T _{W} = 0.764 p U _{INFINITY }^{2}/2 (Re) ^{1/2}

d) T _{W} = 0.664 p U _{INFINITY }^{2}/2 (Re) ^{1/2}.

### View Answer

_{W}= 3 µ U

_{INFINITY}/2 δ = 0.664 p U

_{INFINITY }

^{2}/2 (Re)

^{½}.

7. Boundary layer thickness is given by

a) δ = 5.64 x/ (Re) ^{½}

b) δ = 5.64 x/ (Re) ^{½}

c) δ = 6.64 x/ (Re) ^{½}

d) δ = 7.74 x/ (Re) ^{½}

### View Answer

^{½}(µ/x p U

_{INFINITY})

^{½}.

8. Air at 25 degree Celsius flows over a flat surface with a sharp leading edge at 1.5 m/s. Find the value of Reynolds number. For air at 25 degree Celsius, kinematic viscosity = 15.53* 10n ^{-6} m^{2}/s

a) 38694

b) 12846

c) 48294

d) 76386

### View Answer

_{INFINITY}/v = 48294.

9. A plate 0.3 m long is placed at zero angle of incidence in a stream of 15 degree Celsius water moving at 1 m/s. Find out the maximum value of the normal component of velocity at thr trailing edge of the plate. For water at 15 degree Celsius

p = 998.9 kg /m^{3}

µ = 415.85 * 10 ^{-2} kg/hr m

a) 1.6885 * 10 ^{-2} m/s

b) 1.6885 * 10 ^{-3} m/s

c) 1.6885 * 10 ^{-4} m/s

d) 1.6885 * 10 ^{-5} m/s

### View Answer

_{INFINITY }(Re)

^{½ }=0.860.

## Set 3

1. The relationship (Wavelength) _{MAX} T = constant, between the temperature of a black body and the wavelength at which maximum value of monochromatic emissive power occurs is known as

a) Planck’s law

b) Kirchhoff’s law

c) Lambert’s law

d) Wein’s law

### View Answer

2. A body at 500 K cools by radiating heat to ambient atmosphere maintained at 300 K. When the body has cooled to 400 K, the cooling rate as a percentage of original rate is about

a) 31.1

b) 41.5

c) 50.3

d) 80.4

### View Answer

_{2}/Q

_{1}= (400)

^{4}– (300)

^{4}/ (500)

^{4}– (300)

^{4}= 0.32.

3. Two spheres A and B of same material have radius 1 m and 4 m, and temperatures 4000 K and 2000 K respectively. Then the energy radiated by sphere A is

a) Greater than that of sphere B

b) Less than that of sphere B

c) Equal to that of sphere B

d) Two times that of sphere B

### View Answer

_{ A}/E

_{ B}= (1)

^{2}(4000)

^{4}/ (4)

^{2}(2000)

^{4}= 1.

4. A small body has a total emissive power of 4.5 kW/m^{2}. Determine its surface temperature of maximum emission

a) 530.77 K

b) 345.65 K

c) 236.54 K

d) 367.8 K

### View Answer

^{4}. So, T = 530.77 K.

5. A small black body has a total emissive power of 4.5 k W/m^{2}. In which range of the spectrum does this wavelength fall?

a) Thermal region

b) Cosmic region

c) Visible region

d) Infrared region

### View Answer

^{ -3}. This must be the wavelength of infrared region.

6. The sun emits maximum radiation of 0.52 micron meter. Assuming the sun to be a black body, Calculate the surface temperature of the sun

a) 2345 K

b) 5573 K

c) 9847 K

d) 6492 K

### View Answer

^{ -3}/0.52 * 10

^{-6}= 5573 K.

7. Consider the previous problem, determine the maximum monochromatic emissive power of the sun’s surface

a) 4.908 * 10^{ 13} W/m^{2}

b) 5.908 * 10^{ 13} W/m^{2}

c) 6.908 * 10^{ 13} W/m^{2}

d) 7.908 * 10^{ 13} W/m^{2}

### View Answer

_{ MAX }= 1.285 * 10

^{ -5 }T

^{5}= 6.908 * 10

^{ 13}W/m

^{2}.

8. A furnace emits radiation at 2000 K. Treating it as a black body radiation, calculate the wavelength at which emission is maximum

a) 1.449 * 10^{ -6} m

b) 2.449 * 10^{ -6} m

c) 3.449 * 10^{ -6} m

d) 4.449 * 10^{ -6} m

### View Answer

^{ -3}. So, wavelength = 1.449 * 10

^{ -6}m.

9. Four identical pieces of copper painted with different colors of paints were heated to the same temperature and then left in the environment to cool. Which of the following paint will give fast cooling?

a) White

b) Rough

c) Black

d) Shining

### View Answer

10. A surface for which emissivity is constant at all temperatures and throughout the entire range of wavelength is called

a) Opaque

b) Grey

c) Specular

d) Diathermanous

### View Answer

## Set 4

1. Two black discs each of diameter 50 cm are placed parallel to each other concentrically at a distance of one meter. The discs are maintained at 1000 K and 500 K. Calculate the heat flow between the discs when no other surface is present

a) 317.27 W

b) 417.27 W

c) 517.27 W

d) 617.27 W

### View Answer

_{12}A

_{1 }σ

_{B }(T

_{1 }

^{4 }– T

_{2 }

^{4}).

2. Two black discs each of diameter 50 cm are placed parallel to each other concentrically at a distance of one meter. The discs are maintained at 1000 K and 500 K. Calculate the heat flow between the discs when the disks are connected by a cylindrical black no-flux surface

a) 2417.68 W

b) 3417.68 W

c) 4417.68 W

d) 5417.68 W

### View Answer

_{12}A

_{1 }σ

_{B }(T

_{1 }

^{4 }– T

_{2 }

^{4}).

3. Heat exchange between two black surfaces enclosed by an insulated surface is given by

a) Q _{12} = A _{1} σ _{b }(T _{1}^{4} – T_{2}^{4}) [A _{2 }– A _{1} F _{ 12}^{2}/A _{1} + A _{2 }– 2 A _{1} F _{12}].

b) Q _{12} = 2 A _{1} σ _{b }(T _{1}^{4} – T_{2}^{4}) [A _{2 }– A _{1} F _{ 12}^{2}/A _{1} + A _{2 }– 2 A _{1} F _{12}].

c) Q _{12} = 3 A _{1} σ _{b }(T _{1}^{4} – T_{2}^{4}) [A _{2 }– A _{1} F _{ 12}^{2}/A _{1} + A _{2 }– 2 A _{1} F _{12}].

d) Q _{12} = 4 A _{1} σ _{b }(T _{1}^{4} – T_{2}^{4}) [A _{2 }– A _{1} F _{ 12}^{2}/A _{1} + A _{2 }– 2 A _{1} F _{12}].

### View Answer

4. Heat exchange between two gray surfaces enclosed by an adiabatic surface is given by

a) Q _{12} = A (T_{ 1}^{4 }– T _{2}^{4}) / [1/E _{1} + 1/E_{ 2} – 2 + 2/1 + F _{12}].

b) Q _{12} = A σ _{b} (T_{ 1}^{4 }– T _{2}^{4}) / [1/E _{1} + 1/E_{ 2} + 2/1 + F _{12}].

c) Q _{12} = A σ _{b} (T_{ 1}^{4 }– T _{2}^{4}) / [1/E _{1} + 1/E_{ 2} – 2 + 2/1 + F _{12}].

d) Q _{12} = A σ _{b} (T_{ 1}^{4 }– T _{2}^{4}) / [1/E _{1} + 1/E_{ 2} – 2].

### View Answer

5. A blind cylindrical hole of 2 cm diameter and 3 cm length is drilled into a metal slab having emissivity 0.7. If the metal slab is maintained at 650 K, make calculations for the radiation heat escape from the hole

a) 7 W

b) 3 W

c) 1 W

d) 9 W

### View Answer

_{1}A

_{1}σ

_{b}T

_{ 1}

^{4}[1 – F

_{ 11}/1 – (1 – E

_{1}) F

_{11}].

6. A cavity in the shape of a frustum of a cone has diameter 30 cm and 60 cm and the height is 80 cm. If the cavity is maintained at temperature of 800 K, determine the heat loss from the cavity when the smaller diameter is at the bottom

a) 6577 W

b) 2367 W

c) 8794 W

d) 3675 W

### View Answer

_{1}A

_{1}σ

_{b}T

_{ 1}

^{4}[1 – F

_{ 11}/1 – (1 – E

_{1}) F

_{11}].

7. Consider the above problem, find how this heat loss would be affected if the cavity is positioned with bigger diameter at the base

a) 75.06 % (increase)

b) 55.06 % (decrease)

c) 65.06 % (increase)

d) 75.06 % (decrease)

### View Answer

8. A conical cavity of base diameter 15 cm and height 20 cm has inside surface temperature 650 K. If emissivity of each surface is 0.85, determine the net radiative heat transfer from the cavity

a) 168.3 W

b) 158.3 W

c) 148.3 W

d) 138.3 W

### View Answer

_{1}A

_{1}σ

_{b}T

_{ 1}

^{4}[1 – F

_{ 11}/1 – (1 – E

_{1}) F

_{11}]. Here, F

_{11}= 0.649 and A

_{1}= 0.0503 m

^{2}.

9. A cylindrical cavity of base diameter 15 cm and height 20 cm has inside surface temperature 650 K. If emissivity of each surface is 0.85, determine the net radiative heat transfer from the cavity

a) 194 W

b) 184 W

c) 174 W

d) 164 W

### View Answer

_{1}A

_{1}σ

_{b}T

_{ 1}

^{4}[1 – F

_{ 11}/1 – (1 – E

_{1}) F

_{11}]. Here, F

_{11}= 0.842 and A

_{1}= 0.11186 m

^{2}.

10. What is the unit of coefficient of radiant heat transfer?

a) W/K

b) W/m^{2} K

c) W/m^{2}

d) W/m K

### View Answer

## Set 5

1. The total radiant energy leaving a surface per unit time per unit surface area is represented by

a) Radiation

b) Radiosity

c) Irradiation

d) Interchange factor

### View Answer

2. Determine the radiant heat flux between two closely spaced, black parallel plates radiating only to each other if their temperatures are 850 K and 425 K. The plates have an area of 4 m^{2}

a) .040

b) .030

c) .020

d) .010

### View Answer

_{12}= F

_{12 }A

_{1}σ

_{b}(T

_{1}

^{4}– T

_{2}

^{4}) = .010.

3. What is the value of grey body factor for concentric cylinders?

a) 3/ [1 – e _{1}/e_{ 1} + 1 + 1 – e _{2}/e_{ 2} (A _{1}/A _{2})].

b) 4/ [1 – e _{1}/e_{ 1} + 1 + 1 – e _{2}/e_{ 2} (A _{1}/A _{2})].

c) 1/ [1 – e _{1}/e_{ 1} + 1 + 1 – e _{2}/e_{ 2} (A _{1}/A _{2})].

d) 2/ [1 – e _{1}/e_{ 1} + 1 + 1 – e _{2}/e_{ 2} (A _{1}/A _{2})].

### View Answer

_{12}= 1.

4. The net heat exchange between the two grey surfaces may be written as

a) (Q _{12}) _{NET }= E _{b 1 }– E _{b 2}/ (1 – e _{1}/A _{1} e_{ 1} + 1/A _{1 }F _{12} + 1 – e _{2}/A _{2} e_{ 2})

b) (Q _{12}) _{NET }= 2 E _{b 1 }– E _{b 2}/ (1 – e _{1}/A _{1} e_{ 1} + 1/A _{1 }F _{12} + 1 – e _{2}/A _{2} e_{ 2})

c) (Q _{12}) _{NET }= E _{b 1 }– 2 E _{b 2}/ (1 – e _{1}/A _{1} e_{ 1} + 1/A _{1 }F _{12} + 1 – e _{2}/A _{2} e_{ 2})

d) (Q _{12}) _{NET }= 2 E _{b 1 }– 3 E _{b 2}/ (1 – e _{1}/A _{1} e_{ 1} + 1/A _{1 }F _{12} + 1 – e _{2}/A _{2} e_{ 2})

### View Answer

5. The net rate at which the radiation leaves the surface is given by

a) e (E _{b }–_{ }J)/1 – 4 e

b) e (E _{b }–_{ }J)/1 – 3 e

c) e (E _{b }–_{ }J)/1 – 2 e

d) e (E _{b }–_{ }J)/1 – e

### View Answer

6. A ring (E = 0.85) of 8 cm inner and 16 cm outer diameter is placed in a horizontal plane. A small element (E = 0.7) of 1 cm^{2} is placed concentrically 8 cm vertically below the center of the ring. The temperature of the ring is 800 K and that of small area is 400 K. Find the radiant heat gain by the small ring

a) – 10.59 J/hour

b) – 11.59 J/hour

c) – 12.59 J/hour

d) – 13.59 J/hour

### View Answer

_{12 }= (F

_{g})

_{ 12 }A

_{1}σ

_{b}(T

_{1}

^{4 }– T

_{ 2}

^{4}) = A

_{1}σ

_{b}(T

_{1}

^{4 }– T

_{ 2}

^{4})/ (I/E

_{1}– 1) + 1/F

_{ 12}+ (I/E

_{2}– 1) A

_{ 2}/A

_{1}.

7. Two opposed, parallel, infinite planes are maintained at 420 K and 480 K. Calculate the net heat flux between these planes if one has an emissivity of 0.8 and other an emissivity of 0.7

a) 534.86 W/m^{2}

b) 634.86 W/m^{2}

c) 734.86 W/m^{2}

d) 834.86 W/m^{2}

### View Answer

_{12}= (F

_{g})

_{ 12 }A

_{1}σ

_{b}(T

_{1}

^{4 }– T

_{ 2}

^{4}) and (F

_{g})

_{ 12}= 1/ (I/E

_{1}– 1) + 1/F

_{ 12}+ (I/E

_{2}– 1) A

_{ 2}/A

_{1}.

8. Consider the above problem, if temperature difference is doubled by raising the temperature 480 K to 540 K, then how this heat flux will be affected?

a) 1803.55 W/m^{2}

b) 1703.55 W/m^{2}

c) 1603.55 W/m^{2}

d) 1503.55 W/m^{2}

### View Answer

_{2}= 0.59 (5.67 * 10

^{-8}) (540

^{4}– 420

^{4}).

9. The total radiant energy incident upon a surface per unit time per unit area is known as

a) Shape factor

b) Radiosity

c) Radiation

d) Irradiation

### View Answer

10. Which one of the following is true for opaque non-black surface?

a) J = E +2 p G

b) J = E + p G

c) J = 2 E + p G

d) J = ½ E + p G