Solution:
Given $$\frac{Y_{A}}{Y_{B}} = \frac{7}{4} L_{A} =2m A_{A } = \pi R^{2}$$
$$ L_{B} = 1.5 m A_{B} =\pi\left(2mm\right)^{2} $$
$$\frac{F}{A} = Y \left(\frac{\ell}{L}\right) $$
given F and $$\ell$$ are same $$ \Rightarrow \frac{AY}{L} $$ is same
$$ \frac{A_{A}Y_{A}}{L_{A}} = \frac{A_{B}Y_{B}}{L_{B}} $$
$$\Rightarrow \frac{\left(\pi R^{2}\right)\left(\frac{7}{4}Y_{B}\right)}{2} = \frac{\pi\left(2mm\right)^{2} .Y_{B}}{1.5} $$
R = 1.74 mm
