Hydraulic Turbines and Jets MCQ

71. A jet of water, of cross-sectional area 0.005 m² strikes a flat plate normally with a velocity of 15 m/s. If the plate is moving with a velocity of 5 m/s in the direction of jet and away from the jet, what is the force exerted by the jet on the plate?

1. 0.50 N
2. 250 N
3. 0.25 N
4. 500 N

72. A horizontal water jet with a velocity of 10 m/s and cross-sectional area of 10 mm² strikes a flat plate held normal to the flow direction. The density of water is 1000 kg/m³. The total force on the plate due to the jet is

1. 10 N
2. 100 N
3. 1N
4. 0.1 N

73. Jet ratio (m) is defined as the ratio of

1. Diameter of the jet of water to diameter of the Pelton wheel
2. Velocity of vane to velocity of the jet of water
3. Velocity of flow to velocity of the jet of water
4. Diameter of Pelton wheel to diameter of the jet water

74. Study of impact of jets and of velocity triangles is based on Newton’s law which states: Force = mass x acceleration. For practical applications, the following features are emphasized.

1. Change of velocity takes place in time duration.
2. Rather than the “mass’, the ratio of ‘weight’ and ‘g’ is used.
3. Change of velocity normal to the direction of the impacting inflow is also relevant to the computations.

Which of the above are correct?

1. i and ii only
2. i and iii only
3. ii and iii only
4. i, ii and iii

75. Water is supplied from a height of 5.2 m at the rate of 100 lps to a hydraulic ram that delivers 7 lps to a height of 24 m above the ram. The head loss at the supply pipe is 0.2 m and the delivery pipe has a loss of 1.0 m. The efficiency of the ram is

1. 22.8 %
2. 29.8%
3. 35.0%
4. 39.6%

76. A turbine develops 500 kW power under a net head of 30 m. If the overall efficiency of the turbine is 0.83, the discharge through the turbine is nearly

1. 3.5 m³/s
2. 3.0 m³/s
3. 2.5 m³/s
4. 2.0 m³/s

77. A rectangular plate, weighing 5 kg is suspended by a hinge on the top horizontal edge. The centre of gravity G of the plate is 10 cm from the hinged end. A horizontal jet of water of area 5 cm², whose axis is 15 cm below the hinge, impinges on the plate with velocity V m/sec. In this condition, the plate deflects from the vertical by 20° (sin 20° = 0.34, cos 20° = 0.94). What will be the jet velocity? Take g = 10 m/sec².

1. 4.9 m/sec
2. 5.2 m/sec
3. 5.5 m/sec
4. 5.7 m/sec

78. Constant efficiency curves are also known as

1. Newton curves
2. Pelton curves
3. Muschel curves
4. Kaplan curves

79. In the inlet part of the jet impinging on a Pelton bucket, the velocity of whirl V_w1 is equal to

1. absolute velocity of jet at inlet V₁
2. relative velocity of jet at inlet V_r1
3. zero
4. none of the above

80. A hydraulic turbine has a discharge of 3 m³/s when operating under a head of 15 m and a speed of 500 rpm. If it is to operate under 12 m of head, the rotational speed will be

1. 600 rpm
2. 559 rpm
3. 447 rpm
4. 400 rpm