Question

The length of a well full of water is 10m, breadth is 6m and depth is 10m. A pump with 80% competency can empty the well in 30 minutes. What is the power of the pump?

Answer 1

The power is work divided by time. The pump needs to lift the entire volume of water to the height of 10 m. The volume is

$$V=lbh.\\ M=\rho V=\rho lbh.\\ W=mgh=\rho lbh^2.\\ P=W/(t\eta),\\ P=\rho lbh^2/(t\eta)=417\text{ W}.$$