Answer
(1)
$T_{1}$ is the only positive and constant torgue
Work Step by Step
Lets write the equation for torque:
$T=\dfrac {\partial l}{\partial t}\Rightarrow T_{1}=\dfrac {\partial }{\partial t}\left( 3t+4\right) =3$
$T_{2}=\dfrac {\partial }{\partial t}\left( -6t^{2}\right) =-12t$
$T_{3}=\dfrac {\partial \left( 2\right) }{\partial t}=0$
$T_{4}=\dfrac {\partial \left( \dfrac {4}{t}\right) }{\partial t}=\dfrac {-4}{t^{2}} $
So we can see only $T_{1}$ is positive and constant. Also, $ T_{1}=3$.
