The figure shows the stress distribution across an internal surface of a rectangular beam of height $30 \: \mathrm{mm}$ and depth $10 \: \mathrm{mm}$. The normal stress distribution is given by the expression $\sigma_{x x}=200 y+500 \mathrm{~N} / \mathrm{mm}^{2} ; y$ is the distance in $\mathrm{mm}$ from the centroidal axis of the beam. Assume that there is no variation in the stress distribution along the $z$ -direction.
Which of the following statements is/are $\textsf{CORRECT}$?
- The net force in the $x$ direction is $150 \: \mathrm{kN}$.
- The net force in the $x$ direction is $75 \: \mathrm{kN}$.
- The net moment about the $z$ axis is $4500\: \mathrm{Nm}$.
- The net moment about the $z$ axis is $2250 \: \mathrm{Nm}$.
