Related Rates: Man and Spotlight

In summary, the conversation is about a 2m tall person walking towards a wall at 1.6 m/s while a spotlight 12 m away from the wall shines at them. The question is how fast the length of their shadow on the wall is decreasing when they are 4m away from the wall. The person tried using trigonometry to solve the problem but had difficulty setting up the equation. The other person suggests thinking about the spot light creating a triangle and then inserting the person to create a second smaller triangle, using the numbers given in the question to set up an equation. Eventually, the person manages to solve the problem.
  • #1
Lancelot59
646
1

Homework Statement


A 2m tall person walks toward toward a wall at 1.6 m/s. A spotlight 12 m away from the wall shines at it. How fast is the length of his shadow on the wall decreasing when he is 4m away from the wall?

I tried a few different things with trig, none of which worked.
 
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  • #2
like what?
 
  • #3
Well, actually I couldn't figure out how to setup the equation to begin with.
 
  • #4
ok so start by drawing a picture, and try and relate the distnace of the man from the light or wall to the height of the shadow - think similar triangles
 
  • #5
Yeah, that's where I run into problems.
 
  • #6
ok so what do you need a hand with?
 
  • #7
How can I go about setting up the problem? How can I go about finding an equation to solve? I understand how to solve these problems, but not how to go about setting up their equations.
 
  • #8
Think about the spot light creating a triangle and then insert the man to create a second smaller triangle. Using the numbers you have in the question, you can get your equation from that by setting the two similar triangles equal to each other - I can't remember the exact name for that, sorry. Ex. base/height of triangle one = base/height of triangle two then cross multiply and solve for your unknown that may or may not start with an s.
 
  • #9
I managed to get it. Sorry it took so long to get back. Thanks for your help!
 

Related to Related Rates: Man and Spotlight

1. What is the concept behind related rates in this scenario?

The concept behind related rates in this scenario is the relationship between the movement of the spotlight and the movement of the man. As the man walks towards or away from the spotlight, the distance between them changes, causing the angle at which the spotlight hits the man to also change. This change in angle can be represented by a derivative, and by finding the rate of change of the angle, we can also determine the rate of change of the distance between the man and the spotlight.

2. How do you set up a related rates problem with the man and spotlight?

To set up a related rates problem with the man and spotlight, you need to identify the variables involved and their rates of change. In this scenario, the variables are the distance between the man and the spotlight, the angle at which the spotlight hits the man, and the rate at which the man is walking. You also need to establish a relationship between these variables, which in this case is the tangent function. By taking the derivative of this relationship, you can set up an equation to solve for the related rates.

3. What is the significance of the Pythagorean theorem in this scenario?

The Pythagorean theorem is significant in this scenario because it relates the distance between the man and the spotlight, the height of the spotlight, and the length of the light beam. By using the Pythagorean theorem, we can create an equation connecting these variables, which allows us to find the value of one variable if we know the values of the other two.

4. How do you solve a related rates problem with the man and spotlight?

To solve a related rates problem with the man and spotlight, you need to first set up an equation using the variables involved and their rates of change. Next, you need to take the derivative of the equation and plug in the known values to solve for the unknown rate of change. It is important to keep track of units and use appropriate differentiation rules, such as the chain rule, when solving related rates problems.

5. What are some real-life applications of related rates?

Related rates have many real-life applications, such as in physics, engineering, and economics. For example, related rates can be used to determine the rate of change of the volume of a balloon as it is being filled with air, or the rate of change of the depth of water in a swimming pool as it is being drained. In economics, related rates can be used to analyze the relationship between supply and demand for a certain product. Overall, related rates are useful in any situation where there is a relationship between changing variables.

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