Firstly, I am so glad I have found this chat - I am applying for an Arkwright scholarship this year and the process is really intimidating particularly because I haven't done a lot of technical work in engineering just a lot of basic broad stuff and no one from my school has ever got one.
Secondly, a cam is a method of translating rotary motion into oscillating or linear motion that moves in a specific and predictable manner. It is best explained visually so I would suggest looking at the BBC bitesize page on it but they are frequently used in engines and novelty toys.
Thirdly, in my fretting about the exam, I have looked into the numbers, apparently about 1300 people applied last year, about 660 got interviews and only 340 actually got scholarships and you have to consider the calibre who put themselves through the application process to start with. But then again someone has to get it.
Good luck everyone.