81. A hydraulic turbine has a discharge of 5 m^{3}/s, when operating under a head of 20 m with a speed of 500 rpm. If it is to operate under a head of 15 m, for the same discharge, the rotational speed in rpm will approximately be

- 334
- 433
- 434
- 243

82. If Thoma’s cavitation factor is less than the critical factor, then the overall efficiency of a reaction turbine will have

- abnormal increase
- no change
- gradual increase
- sharp fall

83. A liquid jet of 30 m/s velocity is striking a single symmetrical moving curved vane at the centre. For maximum efficiency, the velocity of the vane should be

- 30 m/s
- 20 m/s
- 15 m/s
- 10 m/s

84. An unsymmetrical sprinkler has frictionless and equal flow through each of the two nozzles. If the absolute velocities are 6.0 m/s and 9.0 m/s, the ratio of the distances of the nozzles from the rotating shaft

- 9
^{1/2}: 6^{1/2} - 9 : 6
- 9
^{2}:6^{2} - 9
^{3}: 6^{3}

85. The speed of a geometrically similar turbine such that when it is developing 1 kW the total suction head is equal to 1 meter. The speed is known as

- unit speed
- specific speed
- suction specific speed
- critical speed

86. A fluid jet of cross sectional area of a and velocity of v strikes normal to moving plate arranged in series with velocity u and u < v, the actual fluid mass striking is equal to

- ρa(v – u)
- ρau
- ρa(v + u)
- ρav

87. A draft tube is fitted to the exit of a reaction turbine, located at 1.82 m above tail race level. The efficiency of draft tube is 75% and velocity of flow at the entry to draft tube is 10 m/s. The pressure at the entrance section of draft tube is

- -5 m
- -3.82 m
- 10.2 m
- 1.82 m

88. A reaction turbine discharges 35 m^{3}/s under a head of 9 m and with an overall efficiency of 91%. The power developed in kW is

- 286.65
- 37.49
- 3.822
- 2866.5

89. If a certain oil of specific gravity 0.75 is conveyed through a pipe of 100 cm diameter, it encounters a nozzle of diameter 25 cm. By what % does the velocity of flow increase at the nozzle outlet w.r.t. the original velocity?

- 1200
- 1500
- 120
- 150

90. Flow number in turbines is defined as

- Q/ND
- Q/ND
^{2} - Q/ND
^{3} - Q/ND
^{4}