An object with mass \( 500 \, \text{g} \) moves along \( x \)-axis with speed \( v = 4\sqrt{x} \, \text{m}/\text{s} \). The force acting on the object is:
\( 4 \, \text{N} \)
\( 5 \, \text{N} \)
\( 8 \, \text{N} \)
\( 6 \, \text{N} \)