1. **Problem statement:** A pump with an input power of 20 horsepower pumps 70 liters of water per second to a height of 15 meters. The water density is 1000 kg/m³ and gravitational acceleration is $g=10\ \mathrm{m/s^2}$. Each horsepower is 750 watts. We need to find the efficiency (بازده) of the pump in percentage. 2. **Given data:** - Input power $P_{in} = 20$ hp - Flow rate $Q = 70$ liters/second = $70 \times 10^{-3} = 0.07$ m³/s - Height $h = 15$ m - Density $\rho = 1000$ kg/m³ - Gravity $g = 10$ m/s² - 1 hp = 750 watts 3. **Formula for hydraulic power output:** $$P_{out} = \rho g Q h$$ This formula calculates the power used to lift the water. 4. **Calculate output power:** $$P_{out} = 1000 \times 10 \times 0.07 \times 15 = 10500\ \mathrm{watts}$$ 5. **Calculate input power in watts:** $$P_{in} = 20 \times 750 = 15000\ \mathrm{watts}$$ 6. **Calculate efficiency:** $$\text{Efficiency} = \frac{P_{out}}{P_{in}} \times 100 = \frac{10500}{15000} \times 100 = 70\%$$ 7. **Answer:** The efficiency of the pump is 70%, which corresponds to option 1) ۷۰.