I also thought this in the exam, and I worked out the length of AB thinking that the angled cross section was a part of an ellipse. It turned out to be really messy so i then assumed that the angled cross section was an arc of the circle and I ended up getting a much neater answer (which was the correct answer)I'm looking back at 14c the volumes question- and is it actually a circle? DA is r, but AB isn't r so it would be a parabola. It'll be too hard if it was for a 4 marker, and obviously their intent was for a circle but it looks a bit weird to me.
I only used parabolas because the 'radii' weren't the same. One was r and the other was something else. Since the height is bounded by that part of the 'curve', I believed it couldn't be a circle. I still think it's not a circle now.. How ridiculouswhy would you use a parabola when it's a circle?
anyway, i used a circle to find height and triangles to work out width
Agreed.This is actually a VERY easy question. What made it hard for many people was:
1. The question wasn't scaffolded.
2. The variable for integrating wasn't introduced - you had to do that yourselves.
Perhaps in future years people should get practice at doing questions without them being set up for them. In other words, jump straight to the last part (of volume questions at least). After all, doing a scaffolded question is NOT what real maths is about.