I only need part D

$5\mathrm{.}4\mathrm{.}2$ The Method of Sections

Learning Goal:

To apply the method of sections to a truss and determine the unknown forces in specified

members.

If a truss is in equilibrium then every member in the truss must also be in equilibrium. This

principle is used in analyzing a truss using the method of sections. To apply the method of

sections, we use an imaginary cut through members of the truss to expose the forces in

those members as external forces.

$($Figure $1)$

If the free$-$body diagram of the joint on either side of the cut is known, we can apply the

equations of equilibrium to that part of the member to determine the forces at the cut

section. Since only three equilibrium equations $({\displaystyle \underset{?}{\overset{?}{}}}Fx=0,Fy=0,$ and $MO=0)$ can be applied to

the free$-$body diagram of any segment, we should try to select a cut that passes through no

more than three members of the truss in which the forces are unknown. Note that the

moment equation can be written multiple times, but there are still only $3$ independent

equilibrium equations available.

For the Howe bridge truss shown, $d=11ft,F1=2950lb,F2=2150lb,F3=2450lb,$ and $F4=3750$

lb$.$

$($Figure $2)$

Part $C-$ Determining the forces in three members on the left$-$hand side of the truss

Determine the forces in members $HI,BH,$ and $BC.$

Express the magnitudes of the forces in pounds to three significant figures. Separate your answers

with commas.

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