Calculate Height of Light Pole from Shadow Length

AI Thread Summary
To calculate the height of a light pole based on the shadow lengths of a stick and the pole, the relationship between the two can be established using trigonometry. A stick measuring 1.1 meters casts a shadow of 1.3 meters, leading to a calculated angle. By applying the same angle to the light pole's shadow of 5.2 meters, the height of the pole is initially calculated as 4.4 meters. However, the discussion reveals that the correct height is actually 5.5 meters, despite the initial calculations. This highlights the importance of verifying answers in mathematical problems.
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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