To identify the quadratic function related to the square root function \( k(x) = \sqrt{5}x \), we need to consider the relationship between a square root function and its corresponding quadratic function.
The square root function can be rewritten as:
\[ k(x) = \sqrt{5}x \implies k(x)^2 = 5x \]
To find the related quadratic function, we square both sides:
\[ y = k(x) \implies y^2 = 5x \]
This implies that the quadratic function related to \( k(x) \) can be expressed as \( m(x) = 5x^2 \) when we express \( x \) in terms of \( y \), indicating that we are dealing with quadratic functions derived from the square root.
Now we check the given options:
- \( m(x) = 25x^2 \)
- \( m(x) = 15x^2 \)
- \( m(x) = \frac{1}{5} x^2 \)
- \( m(x) = 5x^2 \)
- \( m(x) = 125x^2 \)
The correct identification is:
\[ m(x) = 5x^2 \]
Thus, the correct answer is:
\( m(x) = 5x^2 \).