$4\mathrm{.}1-4\mathrm{.}18$ For the beam shown, derive the expressions for $V$ and $M,$ and draw the shear force and bending moment diagrams. Neglect the weight of the beam.

$Y_1$

FIG. P$4.15$

FIC. P$4\mathrm{.}53$

$*$Don$\text{'}$t need $4\mathrm{.}12*$