A team from Engineers Without Borders constructs a system to supply water to a mountainside village located 1800 m above sea level from a spring in the valley below at 1500 m above sea level.

(a). When the pipe from the spring to the village is full of water, but no water is flowing, what is the pressure difference between the end of the pipe at the spring and the end of the pipe in the village?  

(b). What is the change in gravitational potential energy of a liter of water when it is pumped from the spring to the village? 

(c). What is the minimum amount of work required to pump a liter of water from the spring to the village?