Find the positive value for which the vector r(t)=4t,6t2,6t25\displaystyle \vec{{{r}{\left({t}\right)}}}={\left\langle{4}{t},{6}{t}^{{2}},{6}{t}^{{2}}-{5}\right\rangle} is perpendicular to r(t)\displaystyle \vec{{{r}'{\left({t}\right)}}}.