A prismatic beam (as shown below) has plastic moment capacity of $M_p$, then the collapse load $P$ of the beam is

1. $\dfrac{2M_p}{L} \\$
2. $\dfrac{4M_p}{L} \\$
3. $\dfrac{6M_p}{L} \\$
4. $\dfrac{8M_p}{L}$