Physics

Fluid Mechanics and Hydraulics

361 Questions

Fluid mechanics and hydraulics questions address the principles of fluid flow, pipe resistance, and open channel dynamics. The topics include Bernoulli equation, Navier-Stokes equation, and hydrograph calculations. These concepts are crucial for civil and mechanical engineering competitive examinations.

Fluid flow equationsOpen channel flowPipe frictionHydraulic jumpHydrograph analysis

Fluid Mechanics and Hydraulics Questions

Multiple choice

In the inclined manometer shown in the figure below, the reservoir is large. Its surface may be assumed to remain at a fixed elevation. A is connected to a gas pipeline and the deflection noted on the inclined glass tube is 100 mm. Assuming $\theta$= 30o and the manometric fluid as oil with specific gravity of 0.86, the pressure at A is

  1. 43 mm water (vacuum)

  2. 43 mm water

  3. 86 mm water

  4. 100 mm water
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 $\text{height of manometer fluid in the manometer} \\ \hspace{2cm} = 100 \times sin 30^0 = 50 mm\\ \text{as per Pascal's law}\\ P_A = P_B = \rho gh = 0.86 \times 50 \times 1 = 43 mm \hspace{0.2cm}\text{of water}$

Multiple choice

A frictionless fluid of density r flows through a bent pipe as shown below. If A is the cross sectional area and V is the velocity of flow, the forces exerted on segment 1-2 of the pipe in the x and y directions are, respectively
  1. $\rho AV^2; 0$
  2. $rAV^2; \sqrt{2} \rho AV^2$

  3. 0; 0

  4. $0; \frac{1}{\sqrt{2}} \rho AV^2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 Force = Change in momentum per second. but in the present case at section 1 and section 2 there is no change in either direction of velocity, magnitude of velocity and area of cross-section between section 1 and section 2. So $F_x = 0, F_y =0$

Multiple choice

A steady flow occurs in an open channel with lateral inflow of q m3/s per unit width as shown in the figure. The mass conservation equation is
  1. $\frac{\partial q}{\partial x} = 0$
  2. $\frac{\partial Q}{\partial x} = 0$
  3. $\frac{\partial Q}{\partial x} -q = 0$
  4. $\frac{\partial Q}{\partial x} +q = 0$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For steady flow with lateral inflow, the change in discharge along the channel is equal to the lateral inflow rate. The continuity equation reflects this balance.

Multiple choice

A steep wide rectangular channel takes off from a reservoir having an elevation of 101.2 m. At the entrance, the bottom elevation of the channel is 100 m. If the slope of the channel is increased by 4%, the discharge per unit length in the channel will be

  1. 2.24 m2/s

  2. higher than 2.24 m2/s by 4%

  3. higher than 2.24 m2/s by 2%

  4. choked
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In a steep channel, flow is often governed by normal depth. Using Manning's equation, Q is proportional to the square root of the slope. A 4% increase in slope leads to a 2% increase in discharge.

Multiple choice

A thin flat plate 0.5 m x 0.7 m in size settles in a large tank of water with a terminal velocity of 0.12 m/s. The coefficient of drag$C_D = \frac{1.328}{\sqrt{R_L}}$for a laminar boundary layer and$C_D = \frac{0.072}{(R_L)^{1/5}}$for a turbulent boundary layer, where RL is the plate Reynolds number. Assume $\mu$= 10-3 N-s/m2 and $\rho$= 1000 kg/m3 The submerged weight of the plate is

  1. 0.0115 N

  2. 0.0118 N

  3. 0.0231 N

  4. 0.0376 N
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The submerged weight of the plate equals the drag force at terminal velocity. Calculate the Reynolds number, determine the drag coefficient, and solve for the drag force.