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NEET PHYSICSEasy

Water falls from a height of 60 m at a rate of 15 kg/s to operate a turbine. The losses due to frictional forces are 10% of energy. How much power is generated by the turbine? (g=10 m/s2g = 10 \text{ m/s}^2)

A

8.1 kW

B

10.2 kW

C

12.3 kW

D

7.0 kW

Step-by-Step Solution

To find the power generated by the turbine, we first calculate the total input power available from the falling water and then account for energy losses.

  1. Input Power (PinP_{\text{in}}): Power is defined as the rate of change of energy. For falling water, the input power is the rate at which gravitational potential energy (mghmgh) is delivered. Pin=dmdtghP_{\text{in}} = \frac{dm}{dt} \cdot g \cdot h Given the mass flow rate dmdt=15 kg/s\frac{dm}{dt} = 15 \text{ kg/s}, g=10 m/s2g = 10 \text{ m/s}^2, and h=60 mh = 60 \text{ m}: Pin=15×10×60=9,000 W=9.0 kWP_{\text{in}} = 15 \times 10 \times 60 = 9,000 \text{ W} = 9.0 \text{ kW}

  2. Accounting for Losses: The problem states that 10% of the energy is lost to friction. Therefore, the turbine operates with an efficiency (η\eta) of 90% (0.90.9).

  3. Generated Power (PoutP_{\text{out}}): Pout=Pin×ηP_{\text{out}} = P_{\text{in}} \times \eta Pout=9.0 kW×0.9=8.1 kWP_{\text{out}} = 9.0 \text{ kW} \times 0.9 = 8.1 \text{ kW}

Thus, the power generated by the turbine is 8.1 kW.

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