A block of mass \( m \) is placed on a surface having vertical cross section given by \( y=\dfrac{x^{2}}{4} \). If coefficient of friction is \( 0.5 \), the maximum height above the ground at which block can be placed without slipping is:
\( \dfrac{1}{3} \, \text{m} \)
\( \dfrac{1}{2} \, \text{m} \)
\( \dfrac{1}{6} \, \text{m} \)
\( \dfrac{1}{4} \, \text{m} \)