Let's proceed with calculating the forces in members E-F, L-F, and L-M of the truss structure.

### Step 1: Calculate the Support Reactions

We'll start by determining the reaction forces at the supports (H and O). For this, we will:

1. **Sum of moments about point O:**
   - The truss is symmetrical, and there's a vertical load of 200 kg at point L. We assume the lengths between each joint (I to J, J to K, etc.) are equal, so the distance from H to L is \(6 \times 2 \, \text{m} = 12 \, \text{m}\), and from O to L is \(4 \, \text{m}\).
   - Convert the mass to force: \( 200 \times 9.81 \, \text{N} = 1962 \, \text{N} \).

   Taking moments about point O:
   \[
   \sum M_O = 0 \Rightarrow R_H \times 16 \, \text{m} = 1962 \, \text{N} \times 4 \, \text{m}
   \]
   Solving for \(R_H\):
   \[
   R_H = \frac{1962 \times 4}{16} = 490.5 \, \text{N}
   \]

2. **Sum of vertical forces:**
   \[
   \sum F_y = 0 \Rightarrow R_H + R_O = 1962 \, \text{N}
   \]
   \[
   R_O = 1962 - 490.5 = 1471.5 \, \text{N}
   \]

### Step 2: Analyze Joints for Member Forces

We'll use the **Method of Joints** starting from joints that have fewer unknown forces.

#### Joint E:
At joint E, let's assume the forces in the members are tensile (positive direction). The equations for equilibrium are:
- Horizontal equilibrium (\(\sum F_x = 0\)):
  \[
  F_{EF} \cos(45^\circ) = 0
  \]
- Vertical equilibrium (\(\sum F_y = 0\)):
  \[
  F_{EF} \sin(45^\circ) = 0
  \]

Given that joint E is a pin, and there are no horizontal or vertical loads directly at E, this means \(F_{EF} = 0\). Therefore, **member E-F is a zero-force member**.

#### Joint F:
At joint F, considering the forces in members F-E and F-L:
- Horizontal equilibrium (\(\sum F_x = 0\)):
  \[
  F_{LF} \cos(45^\circ) = 0
  \]
- Vertical equilibrium (\(\sum F_y = 0\)):
  \[
  F_{LF} \sin(45^\circ) = R_H = 490.5 \, \text{N}
  \]
Solving for \(F_{LF}\):
\[
F_{LF} = \frac{490.5 \, \text{N}}{\sin(45^\circ)} = 693.8 \, \text{N}
\]

So, **\(F_{LF} = 693.8 \, \text{N}\)**, which is a compressive force.

#### Joint L:
At joint L, which has three members connected (L-F, L-K, L-M):
- Vertical equilibrium (\(\sum F_y = 0\)):
  \[
  F_{LF} \sin(45^\circ) + F_{LM} \sin(45^\circ) = 1962 \, \text{N}
  \]
- Horizontal equilibrium (\(\sum F_x = 0\)):
  \[
  F_{LM} \cos(45^\circ) = F_{LF} \cos(45^\circ)
  \]
Substituting \(F_{LF}\):
\[
F_{LM} \cos(45^\circ) = 693.8 \, \text{N} \times \cos(45^\circ)
\]
This implies \(F_{LM} = 693.8 \, \text{N}\), as well.

So, **\(F_{LM} = 693.8 \, \text{N}\)**, which is also a compressive force.

### Summary of Results:
- **Member E-F**: \(0 \, \text{N}\) (Zero-force member)
- **Member L-F**: \(693.8 \, \text{N}\) (Compressive)
- **Member L-M**: \(693.8 \, \text{N}\) (Compressive)

Would you like further details or explanations on any of these calculations?

---

### Follow-Up Questions:
1. How are zero-force members identified in a truss structure?
2. What assumptions are typically made when analyzing truss structures?
3. How does the Method of Sections differ from the Method of Joints?
4. What are the key factors affecting the stability of a truss structure?
5. How can symmetry simplify the calculation of forces in truss structures?

### Tip:
When solving truss problems, always start with the supports to determine the reaction forces, then proceed to analyze joints or sections with the fewest unknowns to simplify the calculations.

Learn how to calculate the forces in truss members E-F, L-F, and L-M using the Method of Joints and static equilibrium principles. This detailed guide includes step-by-step calculations for each member, identifying zero-force members and determining compressive forces. Suitable for undergraduate-level engineering students and enthusiasts.

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