A force of 50N is applied perpendicularly on three different contact surfaces against a wooden plank:
A. The pointed tip of a drawing pin with contact area 0.5mm2
B. The flat head of the same pin with contact area 25mm2
C. A small wooden block face with contact area 400mm2
a. (i) Arrange the three cases A, B and C in descending order of pressure exerted on the plank.
b. (ii) Justify the order obtained using the relation between pressure and area. You may show proportional reasoning or brief numerical comparison.
c. (iii) Explain why the drawing pin is always used with the pointed end, not with the flat head, when fastening papers to a board.