Which one is more elastic, steel or plastic ? Why ?
$\mathrm{Y}_{\mathrm{S}}=\frac{\mathrm{Fl}}{\mathrm{A} \Delta l_{\mathrm{S}}}$ and $\mathrm{Y}_{\mathrm{E}}=\frac{\mathrm{Fl}}{\mathrm{A} \Delta l_{\mathrm{E}}}$
where both having same length $l$ and deforming force $F$,
$\therefore \frac{\mathrm{Y}_{\mathrm{S}}}{\mathrm{Y}_{\mathrm{E}}}=\frac{\Delta l_{\mathrm{E}}}{\Delta l_{\mathrm{S}}}$
but $\Delta l_{\mathrm{E}}>\Delta l_{\mathrm{S}}$
$\therefore \frac{\mathrm{Y}_{\mathrm{S}}}{\mathrm{Y}_{\mathrm{E}}}>1$
$\therefore \mathrm{Y}_{\mathrm{S}}>\mathrm{Y}_{\mathrm{E}}$ hence, steel is more elastic than plastic.
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