You and your friend, Xoli, are walking in a desert, and come to the top of a deep river valley. You estimate that the water lies 11 m below you. The following conversation occurs:

Xoli: "Ah! If only we could make a very long straw, we could suck up the water from the river down there." You: "That wouldn't work. The laws of physics don't allow that to happen." Xoli: "But that's ridiculous! You just have to suck very hard!"

a)Explain to Xoli the basic principle behind how a straw works. (2)

b)Draw a diagram of a straw in a liquid. Let your diagram look similar to a diagram of a barometer. (1)

c)Use a mathematical argument to prove to Xoli that the highest she can suck the water is 10.3 m (for 0 = 101 300 Pa). Make sure that all the variables you use are labelled on your diagram. (4)