Which analysis method uses cutting through the truss to form a free-body diagram of a section to solve for unknown member forces?

Which analysis method uses cutting through the truss to form a free-body diagram of a section to solve for unknown member forces?

• A. Method of joints
• B. The method of sections
• C. Zero force member
• D. A redundant joint

Answer: (B)

The idea being tested is isolating a portion of the truss by cutting through it and using equilibrium on that isolated section to find the member forces. This method of sections works by cutting through the truss so you can treat one section as a free body, including the forces from the cut members as unknowns, and then apply sum of forces in the x and y directions (and, if helpful, sum of moments) to solve for those unknowns. It’s especially handy when you want the forces in specific members and can choose a cut that passes through those members, ideally keeping the number of unknowns manageable (up to three is typical for a single cut using only two force equations plus a moment equation). The other options aren’t analysis methods that rely on cutting a section; zero-force members are members that carry no load under certain conditions, and a redundant joint is a joint with more unknowns than equations, not a method for solving member forces.

The idea being tested is isolating a portion of the truss by cutting through it and using equilibrium on that isolated section to find the member forces. This method of sections works by cutting through the truss so you can treat one section as a free body, including the forces from the cut members as unknowns, and then apply sum of forces in the x and y directions (and, if helpful, sum of moments) to solve for those unknowns. It’s especially handy when you want the forces in specific members and can choose a cut that passes through those members, ideally keeping the number of unknowns manageable (up to three is typical for a single cut using only two force equations plus a moment equation). The other options aren’t analysis methods that rely on cutting a section; zero-force members are members that carry no load under certain conditions, and a redundant joint is a joint with more unknowns than equations, not a method for solving member forces.