A mirror is placed 35 feet from the base of a waterfall by a hiker. The hiker walks backwards until they are 7.5 feet from the mirror. Determine how tall the waterfall is if the hiker is 6 feet tall.

45 ft
38 ft
28 ft
24 ft

1 answer

To determine the height of the waterfall, we can use the concept of similar triangles.

  1. Let's outline the scenario:

    • The hiker is 6 feet tall.
    • The distance from the hiker to the mirror is 7.5 feet.
    • The distance from the base of the waterfall to the mirror is 35 feet.
  2. The setup creates two similar triangles:

    • Triangle 1 (the hiker's triangle): The height of the hiker is 6 feet, and the distance from the hiker to the mirror is 7.5 feet.
    • Triangle 2 (the waterfall's triangle): The height we want to find, which we'll call \( h \), and the distance from the waterfall to the mirror is 35 feet.
  3. Set up the proportion based on the similarity of the triangles:

    \[ \frac{\text{Height of Hiker}}{\text{Distance from Hiker to Mirror}} = \frac{\text{Height of Waterfall}}{\text{Distance from Waterfall to Mirror}} \]

    Plugging in the known values:

    \[ \frac{6 \text{ ft}}{7.5 \text{ ft}} = \frac{h}{35 \text{ ft}} \]

  4. Cross-multiply to solve for \( h \):

    \[ 6 \cdot 35 = 7.5 \cdot h \]

    \[ 210 = 7.5h \]

  5. Divide both sides by 7.5 to isolate \( h \):

    \[ h = \frac{210}{7.5} \]

    Simplifying:

    \[ h = 28 \text{ ft} \]

Therefore, the height of the waterfall is 28 feet.