Efficiency Questions

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

A $220\text{-volt}$ input is supplied to a transformer. The output circuit draws a current of $2.0\text{ ampere}$ at $440\text{ volts}$. If the efficiency of the transformer is $80\%$, the current drawn by the primary windings of the transformer is:

A $200\text{W}$ sodium street lamp emits yellow light of wavelength $0.6\mu \text{m}$. Assuming it to be $25\%$ efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is: