Calculate Height of Light Pole from Shadow Length

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Homework Help Overview

The problem involves calculating the height of a light pole based on the lengths of shadows cast by a vertical stick and the pole itself. The context is rooted in trigonometry and the relationships between similar triangles formed by the stick and its shadow compared to the light pole and its shadow.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the use of trigonometric relationships to determine the height of the light pole based on the known height of the stick and the lengths of their respective shadows. There is a focus on the assumption that the angles formed by the shadows and the heights are equal due to parallel light rays from the Sun.

Discussion Status

There is an ongoing exploration of the calculated height of the light pole, with some participants agreeing on the initial calculation of 4.4 meters. However, alternative answers are also mentioned, leading to questions about the correctness of the calculations and the possibility of other valid answers.

Contextual Notes

Participants express uncertainty regarding the correctness of the calculated height and mention potential discrepancies with provided answers. The discussion reflects a lack of consensus on the correct height, with multiple values being proposed.

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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