Answer:
When
tree bends, torque acting on the tree due to its weight \[W=Wd\]
\[\therefore
\]\[Wd=\frac{Y\pi {{r}^{4}}}{4R}\]
From
figure, \[{{R}^{2}}={{\left( \frac{h}{2} \right)}^{2}}+{{(R-d)}^{2}}\]
\[=\frac{{{h}^{4}}}{4}+{{R}^{2}}+{{d}^{2}}-2Rd\]
Since
\[d<<R,\] so
\[{{d}^{2}}\] can
be neglected
\[\therefore
\]\[2Rd=\frac{{{h}^{2}}}{4}\]or \[d=\frac{{{h}^{2}}}{8R}\]
Put
this value in eqn. (i), we get
\[\frac{W{{h}^{2}}}{8R}=\frac{Y\pi
{{r}^{4}}}{4R}\] or
\[h=\sqrt{\frac{2Y\pi {{r}^{3}}}{W}}\]
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