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Everytime I try this question I keep getting 93.75 mm. I was just wondering where I'm going wrong. Here's my work:

$$ BC=\dfrac{FL}{AE}=\dfrac{1500000\text{ N}\cdot 1250\text{ mm}}{100000\text{ mm}^2*200\text{ MPa}}=93.75\text{ mm} $$ For deflection to be in $\text{mm}$, all units have to be in $\text{N}$ and $\text{mm}$, right?

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You are correct. The book probably meant $E = 200\text{ GPa}$, which is frequently adopted for steel.

To confirm, I made a simple little model:

enter image description here

You're probably aware of this, but just to make it explicit: your math only worked because $200\text{ MPa} = 200\text{ N/mm}^2$.

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  • $\begingroup$ yeah ok i thought it was something like that and yes i know that MPa is N/mm^2 so everything cancels out to leaves mm. Thanks again $\endgroup$ Oct 31 '16 at 1:31

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