Calculate Height of Light Pole from Shadow Length

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SUMMARY

The height of the light pole can be calculated using similar triangles based on the lengths of the shadows. Given a stick of 1.1 meters casting a shadow of 1.3 meters, the height of the light pole, which casts a shadow of 5.2 meters, is determined to be 5.5 meters. The calculation involves establishing the angle of elevation using trigonometric ratios, specifically tangent, where the ratio of the height to shadow length remains constant. Despite initial calculations suggesting a height of 4.4 meters, the consensus confirms that the correct height is 5.5 meters.

PREREQUISITES
  • Understanding of basic trigonometry, specifically tangent ratios.
  • Familiarity with the concept of similar triangles.
  • Ability to solve equations involving ratios.
  • Knowledge of shadow length and its relationship to height in physics.
NEXT STEPS
  • Review trigonometric functions and their applications in real-world scenarios.
  • Study the properties of similar triangles in geometry.
  • Practice solving problems involving shadow lengths and heights using trigonometry.
  • Explore the concept of angle of elevation and its practical applications.
USEFUL FOR

Students studying geometry and trigonometry, educators teaching physics concepts related to light and shadows, and anyone interested in practical applications of mathematical principles.

lbwet
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Homework Statement


At the outside, there is a vertical stick with a length of 1.1 meter and its shadow on the surface of an Earth is 1.3 meter, there also is light pole and its shadow length is 5.2 meters, what is the height of that light pole?

Homework Equations


Trigonometry equations to relate height one to height two.

The Attempt at a Solution


I drew a right triangle, one leg being 1.1 meter, which is the length of a stick, and another leg being 1.3 meter, which is the length of the shadow. Let angle which is between 1.3 meter side and hypotenuse be alpha, so tangent alpha=1.1/1.3. Now I drew another right triangle, one leg being 5.2 meters (shadow length) and another x, which essentially is the height of the light pole. Because light rays emitted from the Sun on the surface of an Earth is almost parallel (because of big distance between the Sun and an Earth), I can say that an angle between 5.2 meters side and hypotenuse will also be alpha, thus x/5.2=1.1/1.3, now solving for x I get 4.4 meters, but I checked the answer and that does not seem to be right answer.
 
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lbwet said:
now solving for x I get 4.4 meters, but I checked the answer and that does not seem to be right answer.

Your answer makes sense, I also calculated 4.4 m. What are a the other possible answers?
 
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stockzahn said:
Your answer makes sense, I also calculated 4.4 m. What are a the other possible answers?
Other possible answers are:
5.2 m; 5.3 m; 5.5 m; 5.8 m.

And from answers, it says that the correct one is 5.5 m.
 
lbwet said:
it says that the correct one is 5.5 m.
Clearly 4.4 m is correct.
 
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haruspex said:
Clearly 4.4 m is correct.
Thanks, I had doubt but now I'm sure of my answer.
 

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