Question
(a) The “lead” in pencils is a graphite composition with a Young's modulus of about $1 \times 10^9 \textrm{ N/m}^2$. Calculate the change in length of the lead in an automatic pencil if you tap it straight into the pencil with a force of 4.0 N. The lead is 0.50 mm in diameter and 60 mm long. (b) Is the answer reasonable? That is, does it seem to be consistent with what you have observed when using pencils?

$1.2 \textrm{ mm}$

Solution Video