An extension ladder is leaned against a vertical wall with the top contact point 20 feet above grade. What is the minimum distance the base must be from the wall?

An extension ladder is leaned against a vertical wall with the top contact point 20 feet above grade. What is the minimum distance the base must be from the wall?

• A. 4 feet
• B. 3 feet
• C. 6 feet
• D. 5 feet

Answer: (D)

To keep a ladder stable, aim for a safe lean angle around 75 degrees. A widely used rule of thumb is the 4-to-1 rule: for every 4 feet of vertical rise, place the base about 1 foot from the wall. With the top contact 20 feet up, the base distance should be 20 ÷ 4 = 5 feet. This setup gives a ladder length around sqrt(20^2 + 5^2) ≈ 20.6 feet, which is typical for an extension ladder reaching 20 feet. If the base were closer than 5 feet, the ladder would be steeper and less stable; if farther away, the reach would be less practical. Therefore, the minimum base distance is 5 feet.

To keep a ladder stable, aim for a safe lean angle around 75 degrees. A widely used rule of thumb is the 4-to-1 rule: for every 4 feet of vertical rise, place the base about 1 foot from the wall. With the top contact 20 feet up, the base distance should be 20 ÷ 4 = 5 feet. This setup gives a ladder length around sqrt(20^2 + 5^2) ≈ 20.6 feet, which is typical for an extension ladder reaching 20 feet. If the base were closer than 5 feet, the ladder would be steeper and less stable; if farther away, the reach would be less practical. Therefore, the minimum base distance is 5 feet.