고체역학 (Beer) — Shearing Stresses in Beams: Problem 6.1

6.1 A square box beam is made of two $\frac{3}{4} \times 3.5$-in. planks and two $\frac{3}{4} \times 5$-in. planks nailed together as shown. Knowing that the spacing between the nails is $s = 1.25$ in. and that the vertical shear in the beam is $V = 250$ lb, determine (a) the shearing force in each nail, (b) the maximum shearing stress in the beam.