\textbf{155-} The cross-sectional area of a string is $2\,\text{mm}^2$ and its density is $8\,\dfrac{\text{g}}{\text{cm}^3}$. If the wave propagation speed in the string is $25\,\dfrac{\text{m}}{\text{s}}$, what is the tension in the string in Newtons?
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(1) $10$ \hfill (2) $20$ \hfill (3) $100$ \hfill (4) $200$
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