Question

Please solve my previous. questions also it's important for me ​

Answer 1

net head on the other hand is a pressure on the bottom of your pipeline when water is actually flowing to your turbine and always will be lesser than the gross head by your measure due to energy losses by your pipeline
gross head is total vertical distance between intake and turbine.The gross head is reduce over the length of the penstock by friction and turbulence loss.

Answer 2

a) The hydraulic losses through the turbine and draft tube are accounted for in the turbine efficiency.
b) A pelton wheel has a mean bucket speed of 10 m per second with a jet of water flowing at the rate of 700 litres.