## IES 2015 Fluid Mechanics Solved Questions

**Question #1 **

A jet of water issues from a nozzle with a velocity of 20m/s and it impinges normally on a flat plate moving away from it at 10m/s. If the cross section area of the jet is 0.01 m^{2 }and the density of water is taken as 1000kg/m3 , then the force developed on the plate will be

Answer: (A)

Hydrostatic force on the bottom surface of the tank will be,

$F_b=\rho g(l\times b)\times h$

$F_b=\rho g\times (1\times 2)\times 2$

$F_b=4\rho g(lbh)….(i)$

Hydrostatic force on vertical surfece will be,

$F_v=\rho g(l\times h)\times \frac{h}{2}$

$F_v=\rho g(2\times 2)\times \frac{lh^2}{2} $

$F_v=2\rho g(lh^2)….(ii) $

ratio will be,

$\frac{F_b}{F_v}=\frac{4\rho g(lbh)}{2\rho g(lh^2)}$

$\frac{F_b}{F_v}=\frac{2b}{h}$

$\frac{F_b}{F_v}=1…..(Answer)$

(A) 100N

(B) 200N

(C) 1000N

(D) 2000N

**Question #2**

A two dimensional velocity field is given by $V=(x^2-y^2+x)i-(2xy-y)j$

The convective acceleration at (x, y) = (1, 2) is

(A) 0

(B) 14 units

(C) 2 units

(D) None of the above

**Question #3**

Consider the following remarks pertaining to the irrotational flow:

(1) The Laplace equation of steam function $\frac{\partial^2 \psi}{\partial x^2}+\frac{\partial^2 \psi}{\partial y^2}=0$ must be satisfied for the flow to be potential.

(2) The Laplace equation for the velocity potential $\frac{\partial^2 \phi}{\partial x^2}+\frac{\partial^2 \phi}{\partial y^2}=0$ must be satisfied to fulfil the criterion of mass conservation i.e., continuity equation.Which of the above statements is/are correct?

(A) 1 only

(B) Both 1 and 2

(C) 2 only

(D) Neither 1 nor 2

**Question #4**

Jet pumps are often used in process industry for their

(A) Large capacity

(B) High efficiency

(C) Capacity to transport gases, liquids and mixtures of both

(D) None of the above

**Question #5**

Mainly hydraulic turbines are used to drive the electrical alternators which require maintaining the peripheral speed constant even at part load conditions to avoid the change in frequency of electric power. The governing of the hydraulic turbine is done by

(A) Controlling the flow area

(B) Controlling the Velocity

(C) Using the fly wheel

(D) Combined control flow area and velocity

**Question #6**

A tank of length, breadth and height in the ratio of 2:1:2 is full of water. The ratio of hydrostatic force at the bottom to that at any larger vertical surface is

(A) 1

(B) 4

(C) 2

(D) 3

**Question #7**

Which of the following fluids exhibit a certain shear stress at zero shear strain rate followed by a straight line relationship between shear stress and shear strain rate?

(A) Newtonian fluids

(B) Ideal Bingham plastic fluids

(C) Pseudo-plastic fluids

(D) Dilatent fluids

**Question #8**

What is the specific gravity of a marble stone, which weighs 400 N in air, and 200 N in water? (g = 10m/s^{2})

(A) 8

(B) 6

(C) 4

(D) 2

**Question #9**

What is the intensity of pressure in the following SI units, when specific gravity of mercury is 13.6 and the intensity of pressure is 400 KPa?

(A) 0.3 bar or 4.077 m of water or 0.299 m of Hg

(B) 4 bar of 5.077 m of water or 0.399 m of Hg

(C) 0.3 bar or 5.077 m of water or 0.599 m of Hg

(D) 4 bar or 4.077 m of water or 0.299 m of Hg

**Question #10**

Consider the following statements:

(1) If a small upward displacement is given to a floating body, it results in the reduction of the buoyant force acting on the body

(2) A slight horizontal displacement does not change either the magnitude or the location of the buoyant force

Which of the above statements is/are correct?

(A) Both 1 and 2

(B) 1 only

(C) 2 only

(D) Neither 1 nor 2

**Question #11**

The head loss in a sudden expansion from 8cm diameter pipe to 16 cm diameter pipe in terms of velocity V_{1} in the smaller pipe is

(A) $ \frac{1}{4}\left ( \frac{V_1^2}{2g} \right )$

(B) $ \frac{3}{16}\left ( \frac{V_1^2}{2g} \right )$

(C) $ \frac{1}{64}\left ( \frac{V_1^2}{2g} \right )$

(D) $ \frac{9}{16}\left ( \frac{V_1^2}{2g} \right )$

**Question #12**

A fluid is flowing over a flat plate. At distance of 8 cm from the leading edge, the Reynolds number is found to be 25600. The thickness of the boundary layer at this point is

(A) 1.5mm

(B) 2.5mm

(C) 4.0mm

(D) 5.0mm