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

# OpenStax College Physics Solution, Chapter 5, Problem 31 (Problems & Exercises) (1:30)

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Submitted by shelby.keith on Mon, 02/25/2019 - 20:55

Good solution

Submitted by C-Mak Breezy on Wed, 11/27/2019 - 08:05

How come when I put the equation '0.50x10^-3/2' it gives me 2.5x10^4? Your solution is showing the result as 0.25x10^3. Am I missing something?

Submitted by ShaunDychko on Wed, 11/27/2019 - 10:07

I agree with your calculator. The two figures are the same quantities, expressed differently. If you try subtracting one from the other you'll find the answer is zero, as expected for numbers that are the same quantities. The 0.25x10^3 is something I just did in my head rather than using a calculator.

In reply to by C-Mak Breezy