Question

A three-member truss is simply supported at Q and R, and loaded at P by a horizontal force \( F \) as shown. The force in QR is

• A. 0
• B. \( F \) (tensile)
• C. \( \dfrac{F}{\sqrt{2}} \) (compressive)
• D. \( \sqrt{2}F \) (tensile)

Hint:

When analyzing trusses, the forces in the members can be determined by resolving the applied forces and using equilibrium conditions. The angle between the member and the applied force helps determine the magnitude and direction of the force in the truss members.

Answer 1

The Correct Option is B

In this truss problem, the force in member QR can be determined using the method of joints or equilibrium of forces. - The load at point P creates a reaction force at points Q and R.
- The member QR forms a 45-degree angle with the horizontal, which is important in resolving the forces.
- The horizontal load \( F \) applied at point P results in an equal and opposite tensile force in the truss member QR, which balances the force at point P.
- Since the load at P is horizontal and the force in QR must balance this load, the force in member QR is equal to the applied load \( F \), and it is tensile in nature.
Thus, the correct answer is \( F \) (tensile), as shown in option (B).