GATE 2022 CE (CE2) – Question 57
A pump with an efficiency of 80% is used to draw groundwater from a well for irrigating a flat field of area 108 hectares. The base period and delta for paddy crop on this field are 120 days and 144 cm, respectively. Water application efficiency in the field is 80%. The lowest level of water in the well is 10 m below the ground. The minimum required horse power (h.p.) of the pump is ________. (round off to two decimal places) (Consider 1 h.p. = 746 W; unit weight of water = 9810 N/m3)
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Correct answer: 30.67 to 30.97
Explanation
Net crop water volume is $108(10^4)(1.44)=1555200$ m³. Divide by application efficiency 0.8 and 120×86400 seconds to obtain required discharge Q=0.1875 m³/s.
Pump input power is $\gamma QH/\eta=9810(0.1875)(10)/0.8=22992.1875$ W. Divide by 746 W/hp: **30.82 hp**.