\textbf{158.} The equation of a moving object's path in SI is $y = -\dfrac{1}{5}x^2 + 3x$. If the velocity component along the $x$-axis is constant and equal to $5\,\dfrac{\text{m}}{\text{s}}$, what is the speed of the object (in meters per second) at the moment it passes through point $M(5\text{m},\,10\text{m})$? (The object is at the origin at $t = 0$.)
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(1) $5$ \hfill (2) $5\sqrt{2}$ \hfill (3) $10$ \hfill (4) $10\sqrt{2}$
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