The shear stress at the neutral axis in a beam of triangular section with a base of $$40$$ $$mm$$ and height $$20$$ $$mm,$$ subjected to a shear force of $$3$$ $$kN$$ is

$${\rm I}$$-section of a beam is formed by gluing wooden planks as shown in the figure below. If this beam transmits a constant vertical shear force of $$3000$$ $$N$$, the glue at any of the four joints will be subjected to a shear force (in $$kN$$ per meter length ) of

If a beam of rectangular cross-section is subjected to a vertical shear force $$V,$$ the shear force carried by the upper one-third of the cross-section is