vectors

[matteh]

after revisiting the 2007 paper on extended answer 4, i realise that i have no idea whats going on with question for sections c & d. I know its really late but if anyones gone through it recently and prepared to shed some light that'd be great. My main concerns are;

c) why is a velocity vector being used to find the angle? i would have thought a position vector would have been used, and why is it sin not cos?? confusing
d) they use the dot product of a position vector and velocity vector to = 0, why? and what is the significance of perpindicular velocity/position vectors?


http://www.vcaa.vic.edu.au/vce/studies/mathematics/specialist/exams.html exams here if you dont have a copy on you.