Math Problem Statement

For a project in his Geometry class, Anand uses a mirror on the ground to measure the height of his school’s football goalpost. He walks a distance of 14.75 meters from the goalpost, then places a mirror on flat on the ground, marked with an X at the center. He then steps 1.3 meters to the other side of the mirror, until he can see the top of the goalpost clearly marked in the X. His partner measures the distance from his eyes to the ground to be 1.45 meters. How tall is the goalpost? Round your answer to the nearest hundredth of a meter.

Solution

To solve this problem, we can use the concept of similar triangles. When Anand walks 1.3 meters to the other side of the mirror and sees the top of the goalpost in the reflection, it forms two similar triangles: one formed by the goalpost and Anand's position and the other formed by the reflection and the distance from Anand's eyes to the mirror.

Steps to solve the problem:

  1. Identify the key distances and variables:

    • Distance from the goalpost to Anand's position: 14.75 meters.
    • Distance from Anand to the mirror: 1.3 meters.
    • Anand's eye height: 1.45 meters.
    • Let hh be the height of the goalpost, which we need to find.
  2. Set up the proportion based on similar triangles: The two triangles are similar because the light travels in a straight line and reflects off the mirror. Thus, we can write the following proportional equation: height of goalpostheight of Anand’s eyesdistance from goalpost to mirror=height of Anand’s eyesdistance from Anand to mirror\frac{\text{height of goalpost} - \text{height of Anand's eyes}}{\text{distance from goalpost to mirror}} = \frac{\text{height of Anand's eyes}}{\text{distance from Anand to mirror}}

    Substituting the known values: h1.4514.75=1.451.3\frac{h - 1.45}{14.75} = \frac{1.45}{1.3}

  3. Solve for hh: First, simplify the right-hand side: 1.451.31.115\frac{1.45}{1.3} \approx 1.115

    Now, substitute this into the equation: h1.4514.75=1.115\frac{h - 1.45}{14.75} = 1.115

    Multiply both sides by 14.75 to eliminate the denominator: h1.45=1.115×14.75h - 1.45 = 1.115 \times 14.75 h1.45=16.457h - 1.45 = 16.457

    Now, add 1.45 to both sides: h=16.457+1.45=17.907h = 16.457 + 1.45 = 17.907

  4. Round the result: The height of the goalpost is approximately 17.91\boxed{17.91} meters.

Final Answer:

The height of the goalpost is 17.91 meters when rounded to the nearest hundredth.

Would you like further explanation or assistance with other questions? Here are some related questions to explore:

  1. How does the law of reflection apply in this scenario?
  2. What would happen if the distances from Anand to the mirror or from the mirror to the goalpost were different?
  3. How would the height of the goalpost change if Anand's eye height were different?
  4. How can this technique of using a mirror to measure heights be applied in other situations?
  5. How can trigonometry be used to solve similar problems instead of using similar triangles?

Tip: In problems involving similar triangles, ensure that the corresponding sides are proportional to each other.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Similar Triangles
Proportions
Geometry

Formulas

Proportionality: (height of goalpost - height of eyes) / distance from goalpost to mirror = height of eyes / distance from mirror to Anand

Theorems

Similar Triangles Theorem

Suitable Grade Level

Grades 9-10