Calculate Height of Light Pole from Shadow Length

In summary, the conversation discusses the height of a light pole given the length of its shadow and the length of a stick's shadow. The solution involves using trigonometry to set up two right triangles and finding the height of the light pole using the tangent ratio. The possible answers are 5.2 m, 5.3 m, 5.5 m, and 5.8 m, with the correct answer being 5.5 m. The conversation concludes with confirmation that the correct answer is indeed 4.4 m.
  • #1
lbwet
8
2

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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  • #2
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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  • #3
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.
 
  • #4
lbwet said:
it says that the correct one is 5.5 m.
Clearly 4.4 m is correct.
 
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  • #5
haruspex said:
Clearly 4.4 m is correct.
Thanks, I had doubt but now I'm sure of my answer.
 

1. How do you calculate the height of a light pole from its shadow length?

To calculate the height of a light pole from its shadow length, you will need to use simple trigonometric equations. First, measure the length of the shadow cast by the pole. Then, measure the distance from the base of the pole to the end of the shadow. Finally, divide the length of the shadow by the distance from the base of the pole to get the tangent value. Use the inverse tangent function (arctan) to find the angle. The height of the light pole is equal to the distance from the base of the pole multiplied by the tangent of the angle.

2. What tools do I need to calculate the height of a light pole from its shadow length?

You will need a measuring tape or ruler to measure the length of the shadow and the distance from the base of the pole. You will also need a calculator to perform the necessary mathematical calculations.

3. Can the height of a light pole be calculated without measuring the shadow length?

No, the height of a light pole cannot be accurately calculated without measuring the length of its shadow. The length of the shadow is a crucial component in the trigonometric equations used to calculate the height.

4. Is it necessary to know the exact angle of the sun to calculate the height of a light pole from its shadow length?

No, it is not necessary to know the exact angle of the sun to calculate the height of a light pole from its shadow length. As long as the measurements of the shadow length and distance from the base of the pole are accurate, the resulting height calculation will be accurate.

5. Are there any other factors that may affect the accuracy of the height calculation?

Yes, there are a few factors that may affect the accuracy of the height calculation. These include uneven terrain, the curvature of the earth, and the presence of nearby objects that may cast shadows on the light pole. It is important to take these factors into consideration and make necessary adjustments to ensure an accurate calculation.

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