Answer
$2.5\times10^{-3}\,K$
Work Step by Step
Recall:
Rms speed $v_{rms}=\sqrt {\frac{3k_{B}T}{m}}$ where $m$ is the mass of molecules, $T$ is the temperature and $k_{B}=1.38\times10^{-23}\,J/K$ is the Boltzmann's constant.
For nitrogen molecule, $m=28\,u=28(1.66\times10^{-27}\,kg)=4.65\times10^{-26}\,kg$
Given that $v_{rms}=1.5\,m/s$.
$\implies T=\frac{mv_{rms}^{2}}{3k_{B}}=\frac{(4.65\times10^{-26}\,kg)(1.5\,m/s)^{2}}{3(1.38\times10^{-23}\,J/K)}$
$=2.5\times10^{-3}\,K$
