A drawing pin whose point has a cross-sectional area of 0.11 mm2 is used to pin a notice to a tree, the wood of which requires a pressure of 2000 MPa for penetration. Calculate the force needed.
| Data statements | p
= 2 x 109 Pa
A = 0.11 x 10-6 m2 |
For the area, the squaring applies to the whole of mm, which is translated as (x10-3m)2 |
| Formula | p = F/A | |
| Transposition | F = p A | |
| Substitution | F = 2 x 109 Pa x 0.11 x 10-6 m2 | |
| Evaluation | F = 220 N | the area datum is to 2 sig figs. The pressure datum could be anything from 1 SF to 4 SF. So we'll allow the area datum to prevail. |