Is the Strut a Two Force Member? Why is Only One Force Used in Calculations?

[xzibition8612]

Homework Statement

see attachment

Homework Equations

The Attempt at a Solution

The book says the strut is a two force member. Why then isn't there a equal but opposite direction force Fba at point B? Isn't that what a two force member means? Why for this two-force member only the force at point A is used in the calculations? Thanks.

 

[tiny-tim]

hi xzibition8612!

The book says the strut is a two force member. Why then isn't there a equal but opposite direction force Fba at point B?

there is

but the free body diagram is for the whole thing (bed contents and strut),

so F_ba is not used since it's an internal force

 

[xzibition8612]

damn your smart