# Fluid Mechanics and Machines & Hydrology PYQ – TN TRB Lecturer

1.â€ƒWhen the fluid is at rest, the shear stress is _____ .

**[TN TRB 2012: 1 Mark]**

- Maximum
- Zero
- Unpredictable
- Higher

**Answer:**Option B

**Explanation:**

As per Newtonâ€™s law of viscosity, for a Newtonian fluid, the shear stress is directly proportional to the rate of shear strain. When the fluid is at rest, there is no shear strain. Hence, when the fluid is at rest, the shear strain is zero.

2.â€ƒA current meter is a device used for measuring _____ .

**[TN TRB 2012: 1 Mark]**

- Velocity
- Viscosity
- Current
- Pressure

**Answer:**Option A

**Explanation:**

Current meter is a device used for measuring the stream velocity.

3. â€ƒFor the laminar flow through a circular pipe the ratio of maximum velocity to average velocity is _____ .

**[TN TRB 2012: 1 Mark]**

- 1.5
- 2.5
- 2.0
- 1.0

**Answer:**Option C

**Explanation:**

For a laminar flow through a circular pipe,

Maximum velocity, V_{max} = –

4µ

∂x

R^{2}

Average velocity, V_{avg} = –

8µ

∂x

R^{2}

Hence,

_{max}

V

_{avg}

=

–

4µ

∂x

R^{2}

–

8µ

∂x

R^{2}

⇒

_{max}

V

_{avg}

= 2

4. â€ƒIf the Froude number in open channel flow is equal to 1.0, the flow is called _____ .

**[TN TRB 2012: 1 Mark]**

- Streaming flow
- Tranquil flow
- Shooting flow
- Critical flow

**Answer:**Option D

**Explanation:**

- If Froudeâ€™s number is less than 1, then the flow is sub-critical.
- If Froudeâ€™s number is equal to 1, then the flow is critical.
- If Froudeâ€™s number is greater than 1, then the flow is super-critical.

5. â€ƒSpecific energy of a flowing fluid per unit weight is equal to _____ .

**[TN TRB 2012: 1 Mark]**

- P W
+

V^{2}2g - P W
+ h

h +

V^{2}2g- P W
+

V^{2}2g+ h

**Answer:**Option C

**Explanation:**

The specific energy is the sum of potential head (h) and velocity head (V

^{2}/2g).

where,

h – height of water above the bed,

V – velocity of flow.

6. â€ƒThe dimension for specific weight is _____ .

**[TN TRB 2012: 1 Mark]**

- ML
^{-2}T^{-2} - ML
^{-1}T - MLT
^{2} - ML
^{-1}T^{-2}

**Answer:**Option A

**Explanation:**

Specific weight =

Volume

=

Volume

⇒ Specific weight =

^{-2})

L

^{3}

⇒ Specific weight = ML^{-2}T^{-2}

7. â€ƒAn isohyet is a line joining points of _____ .

**[TN TRB 2012: 1 Mark]**

- Equal rainfall intensity
- Equal storm durations
- Equal rainfall excess
- Equal rainfall depth

**Answer:**Option D

**Explanation:**

An isohyet is a line joining the points of equal rainfall depth.

8. â€ƒDickenâ€™s formula for flood peak is given by _____ .

**[TN TRB 2012: 1 Mark]**

- Q = CA
^{1/3} - Q = CA
^{3/4} - Q = CA
^{1/4} - Q = CA
^{2/3}

**Answer:**Option B

**Explanation:**

Dickenâ€™s formula for peak discharge (Q

_{p}) is,

Q

_{p}= CA

^{3/4}

Where,

C – Dickenâ€™s coefficient

A – Area in km

^{2}

9. â€ƒThere is a minimum wastage of water in _____ .

**[TN TRB 2012: 1 Mark]**

- Sprinkler irrigation
- Furrow irrigation
- Check basin irrigation
- Border method

**Answer:**Option A

**Explanation:**

The wastage of water is minimum,

- In Sprinkler irrigation, the losses due to surface runoff and percolation are eliminated. Efficiency is 80%.
- In drip irrigation, the losses due to evaporation and seepage are eliminated. Efficiency is 90%.

10. â€ƒKhoslaâ€™s safe exit gradient for design of weirs will be the lowest for which of the following soil types ?

**[TN TRB 2012: 1 Mark]**

- Coarse sand
- Gravels
- Fine sand
- Shingles

**Answer:**Option C

**Explanation:**

The value of Khoslaâ€™s safe exit gradient for the design of weirs based on different soil types are given below:

- Shingle – 1/4 to 1/5
- Coarse sand – 1/5 to 1/6
- Fine sand – 1/6 to 1/7