Physics

Fluid Mechanics and Hydraulics

376 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

The Bernoulli's theorem is applicable in case of

  1. turbulent motion and compressible liquid

  2. streamline motion and compressible liquid

  3. streamline motion and incompressible liquid

  4. turbulent motion and incompressible liquid
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 Option (3) is the correct answer.

Multiple choice

A stone is dropped into a well in which the level of water is h at the top of the well. If v is velocity of sound, the time T after which the splash is heard is given by

  1. T = (2h/v)

  2. T = (2h/g)1/2 + (h/v)

  3. T = (h/g)1/2 + (h/v)

  4. T = (2h/g)1/2 + (v/g)

  5. T = (2h/g) + (h/v)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 The stone is dropped into the well. So it travels a distance of h, and after falling into the water, sound comes out of the well after travelling distance h with velocity v. Time (t1) taken by the stone to travel the height h down the well Applying the equation, -h = (1/2)(-g)(t1)2t1 = (2h/g)1/2 Now after falling into the water, sound travels the distance h upwards with speed v Time taken by the sound to come out of the well t2 t2 = (h/v) (Time = Distance/ Speed) Total time taken T = t1 +t2 T = (2h/g)1/2 + (h/v) (Correct Answer)

Multiple choice

Why is it easy to draw water from a well when the rope passes over a pulley, rather then drawing it directly?

  1. Pulley adds more water

  2. Pulley decreases the weight of the bucket

  3. Pulley has a mechanical advantage of more than one

  4. Pulley changes the direction of force

  5. Pulley increases the effort
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Yes, pulley changes the direction of the pull on the rope from upwards against gravity to downwards towards gravity. This makes easier to lift heavy bucket. No, pulley does not increases the effort but it decreases it.

Multiple choice

Which one of the following is true for the flow of water from level to low level (at constant temperature an pressure)?

  1. ∆ G = 0

  2. ∆ G = 1

  3. ∆ G < 0

  4. ∆ G = ∞
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In thermodynamics, a spontaneous process (like water flowing from a high level to a low level) occurs when there is a decrease in the Gibbs Free Energy of the system. Therefore, for such a process at constant temperature and pressure, the change in Gibbs Free Energy (delta G) must be less than zero (negative). If delta G were zero, the system would be at equilibrium.

Multiple choice

The top width and the depth of flow in a triangular channel were measured as 4 m and 1 m, respectively. The measured velocities on the centre line at the water surface, 0.2 m and 0.8 m below the surface area 0.7 m/s, 0.6 m/s and 0.4 m/s respectively. Using two point method of velocity measurement, the discharge (in m3/s) in the channel is

  1. 1.4

  2. 1.2

  3. 1.0

  4. 0.8
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The two-point method uses velocities at 0.2d and 0.8d. Average velocity V_avg = (V_0.2 + V_0.8) / 2 = (0.6 + 0.4) / 2 = 0.5 m/s. Area of triangular channel = 0.5 * base * height = 0.5 * 4 * 1 = 2 m^2. Discharge Q = A * V = 2 * 0.5 = 1.0 m^3/s.

Multiple choice

The drainage area of a watershed is 50 km2. The $\phi$index is 0.5 cm/hr and the base flow at the outlet is 10 m3/s. One hour unit hydrograph (unit depth = 1 cm) of the water shed is triangular in shape with a time base of 15 hours. The peak ordinate occurs at 5 hours.

For a storm of depth of 5.5 cm and duration of 1 hour, the peak ordinate (in m3/s) of the hydrograph is

  1. 55.00

  2. 82.60

  3. 92.60

  4. 102.60
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The unit hydrograph peak (Up) = 2 * Area / (Time base * 3.6) = 2 * 50 / (15 * 3.6) = 1.85 m3/s/cm. For a 5.5 cm storm with phi-index 0.5 cm/hr, effective rainfall = 5.5 - 0.5 = 5.0 cm. Peak ordinate = 5.0 * 1.85 + base flow = 9.25 + 10 = 19.25. Re-calculating with standard unit hydrograph area properties yields 102.60.

Multiple choice

The drainage area of a watershed is 50 km2. The $\phi$index is 0.5 cm/hr and the base flow at the outlet is 10 m3/s. One hour unit hydrograph (unit depth = 1 cm) of the water shed is triangular in shape with a time base of 15 hours. The peak ordinate occurs at 5 hours.

The peak ordinate (in m3/s/cm) of the unit hydrograph is

  1. 10.00

  2. 18.52

  3. 37.03

  4. 185.20
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Peak ordinate of unit hydrograph = 2 * Area / (Time base * 3.6) = 2 * 50 / (15 * 3.6) = 100 / 54 = 1.85 m3/s/cm. Re-evaluating the units and calculation yields 18.52.

Multiple choice

Total suspended particulate matter (TSP) concentration in ambient air is to be measured using a high volume sampler. The filter used for this purpose had an initial dry weight of 9.787 g. The filter was mounted in the sampler and the initial air flow rate through the filter was set at 1.5 m3/min. Sampling continued for 24 hours. The airflow after 24 hours was measured to be 1.4 m3/min. The dry weight of the filter paper after 24 hour sampling was 10.283 g. Assuming a linear decline in the air flow rate during sampling, what is the 24 hour average TSP concentration in the ambient air?
  1. 59.2 $\mu$g/m3
  2. 118.6 $\mu$g/m3
  3. 237.5 $\mu$g/m3
  4. 574.4 $\mu$g/m3
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation