21. The necessary and sufficient condition which brings about separation of boundary layer is
    

    	dp	> 0 (True / False)
    	dx

1. 1. True

   
   
   

   2. False

   
   
   

   3. NA

   
   
   

   4. NA

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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22. The predominant forces acting on an element of fluid in the boundary layer over a flat plate in a uniform parallel stream are

1. 1. Viscous and pressure forces

   
   
   

   2. Viscous and inertia forces

   
   
   

   3. Viscous and body forces

   
   
   

   4. Inertial and pressure forces

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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23. The instantaneous stream wise velocity of a turbulent flow is given as follows: u(x, y, z, t) = u(x, y, z) + u'(x, y, z, t) The time average of the fluctuating velocity u (x, y, z, t) is

1. 1. 	u'
      	2

   
   
   

   2. -	u
      	2

   
   
   

   3. zero

   
   
   

   4. 	u
      	2

   
   
   

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1. View Hint View Answer Discuss in Forum

   Time average of fluctuating velocity is zero.

   Correct Option: C

   Time average of fluctuating velocity is zero.

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24. A frictionless circular piston of area 10^-2m² and mass 100 kg sinks into a cylindrical container of the same area filled with water of density 1000 kg/m³ as shown in the figure. The container has a hole of area 10–3m2 at the bottom that is open to the atmosphere. Assuming there is no leakage from the edges of the piston and considering water to be incompressible, the magnitude of the piston velocity (in m/s) at the instant shown is _________ (correct to three decimal places).
    

1. 1. 1.456 m/s

   
   
   

   2. 2.456 m/s

   
   
   

   3. 3.456 m/s

   
   
   

   4. 4.456 m/s

   
   
   

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1. View Hint View Answer Discuss in Forum

   A₁ V₁ = A₂ V₂

   Correct Option: A

   A₁ V₁ = A₂ V₂

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25. A tank open at the top with a water level of 1 m, as shown in the figure, has a hole at a height of 0.5 m. A free jet leaves horizontally from the smooth hole. The distance X(in m) where the jet strikes the floor is
    

1. 1. 0.5

   
   
   

   2. 1.0

   
   
   

   3. 2.0

   
   
   

   4. 4.0

   
   
   

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1. View Hint View Answer Discuss in Forum

   u_x = √2gh
   
   = √2 × 9.8 × 0.5
   u_x = 3.13 m/s
   Now for distance x
   we require u_x so–
   

   x = ux . t +	1	× a × b
   	2

   
   x = 3.13 t
   (∵ acceleration (a) = 0 in horizontal direction)
   

   Now for t ⇒ y = uyt +	1	gt²
   	2

   
   

   ⇒ 0.5 = 0 +	1	× 9.81 × t² [∵ uy = 0]
   	2

   
   t = 0.319 sec.
   so distance, x = 3.13 × 319 = 1m

   Correct Option: B

   u_x = √2gh
   
   = √2 × 9.8 × 0.5
   u_x = 3.13 m/s
   Now for distance x
   we require u_x so–
   

   x = ux . t +	1	× a × b
   	2

   
   x = 3.13 t
   (∵ acceleration (a) = 0 in horizontal direction)
   

   Now for t ⇒ y = uyt +	1	gt²
   	2

   
   

   ⇒ 0.5 = 0 +	1	× 9.81 × t² [∵ uy = 0]
   	2

   
   t = 0.319 sec.
   so distance, x = 3.13 × 319 = 1m

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