A uniform ladder 6.5 m long and of weight 250 N leans on a smooth wall, with its foot 2.5 m from…

Step 1. Torques. $N_{\text{wall}} \times 6.0\ \text{m} = 250\ \text{N} \times 1.25\ \text{m} + 700\ \text{N} \times 2.0\ \text{m} = 1712.5\ \text{N\,m}$, so $N_{\text{wall}} = 285.4\ \text{N}$.

Step 2. Forces. Horizontally, friction $= N_{\text{wall}} = 285.4\ \text{N}$. Vertically, the floor pushes up $950\ \text{N}$.

Step 3. Coefficient. $\mu \ge \dfrac{285.4\ \text{N}}{950\ \text{N}} = 0.300$.