Fluid Mechanics and Machines & Hydrology PYQ – TN TRB Lecturer
41. Rainfall intensity of 20 mm/hr occurred over a watershed of area 100 ha for a duration of 6 hr. Measured Direct Runoff volume in the stream draining the watershed was found to be 30000 m3. The precipitation not available to runoff in this case is _____ .
[TN TRB 2021: 2 Marks]
- 9 cm
- 3 cm
- 17.5 mm
- 5 mm
Explanation:
Total Rainfall = 20 x 6 = 120 mm
Direct Runoff =
Watershed area
=
100 x 104
= 0.03 m (or) 30 mm
Thus, the precipitation not available for runoff = Total Rainfall – Direct Runoff = 120 – 30 = 90 mm (or) 9 cm
42. In the Muskingum method of channel routing, if the coefficients k = 12 hr, x = 0.15 and the time step for routing Δt = 4 hr, then the coefficient C0 is _____ .
[TN TRB 2021: 2 Marks]
- 0.656
- 0.328
- 0.048
- 0.016
Explanation:
C0 =
K(1 – x) + 0.5Δt
⇒ C0 =
12 (1 – 0.15) + (0.5 x 4)
⇒ C0 = 0.016
43.  A rectangular plate 3 m long and 1 m wide is immersed vertically in water in such a way that it’s 3 m side is parallel to the water surface and is 1 m below it. The total pressure on the plate is _____ .
[TN TRB 2021: 2 Marks]
- 44.14 kN
- 34.14 kN
- 24.14 kN
- 14.14 kN
Explanation:
Centroid, h = 1 + (1/2) = 1.5 m
Total pressure, F = ρgAh = 1000 x 9.81 x (3 x 1) x 1.5
⇒ F = 44145 N (or) 44.145 kN
44.  If the x-component of velocity u = 6xy – 2x2 in a possible case of flow, the y-component of the flow v is _____ .
[TN TRB 2021: 2 Marks]
- 6y2 – 4xy
- -6xy + 2x2
- 6x2 – 2xy
- 4xy – 3y2
Explanation:
u = 6xy – 2x2
⇒
∂x
= 6y – 4x
For a possible case of flow, a continuity equation must exist.
∂x
+
∂y
= 0
⇒ 6y – 4x +
∂y
= 0
⇒
∂y
= 4x – 6y
Integrating with respect to y,
⇒ v = 4xy –
2
⇒ v = 4xy – 3y2