• shanshan
In summary, the conversation discusses a man's height and distance from a light source, and the rate at which his shadow is lengthening. The solution involves using similar triangles to find the relationship between the shadow length and distance from the light source. The conversation ends with the understanding that the relationship between the man's walking speed and shadow length is constant.

## Homework Statement

A man 6m tall walks away from a light 10m above the ground. If his shadow lengthens at a rate of 2m/s, how fast is he walking?

## The Attempt at a Solution

I have nothing.

Using similar triangles you can find the relationship between the shadow length (B) and distance away from pole (A).

Keeping in mind that you are given dB/dt and asked to find dA/dt

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but how can i use similar triangles if i only have one of the dimensions of the triangle?

shanshan said:
but how can i use similar triangles if i only have one of the dimensions of the triangle?

Look at the picture I attached. The relationship between ratios is constant, therefore the relationship between speed of man and length of shadow is constant

ahhhh and the light goes on. thankyou!

## 1. What are related rates questions?

Related rates questions involve finding the rate of change of one quantity with respect to another, typically involving multiple variables that are changing over time. In other words, it is a type of problem where you are given the rates of change of two or more variables and you need to find the rate of change of a third variable that is related to those variables.

## 2. How do you solve related rates questions?

To solve related rates questions, you need to first identify the variables involved and their rates of change. Then, you need to use the given information and the chain rule to set up an equation relating the rates of change. Finally, you can solve for the desired rate of change by plugging in the known values and solving for the unknown rate.

## 3. What is the chain rule and why is it important in related rates questions?

The chain rule is a calculus rule that enables us to find the derivative of a composite function. In related rates questions, we often encounter situations where the rates of change of different variables are related through a chain of functions. The chain rule allows us to break down the composite function into smaller, more manageable parts in order to solve for the desired rate of change.

## 4. How do shadows relate to related rates questions?

In related rates questions involving shadows, the rate of change of the length of a shadow is typically related to the rate of change of the height of an object and the angle of the sun's rays. These types of questions require us to use trigonometry and the chain rule to solve for the rate of change of the length of the shadow.

## 5. Can you provide an example of a related rates question involving shadows?

Sure! An example of a related rates question involving shadows would be: A 10-foot-tall streetlight casts a shadow that is 15 feet long. If the sun is setting at a rate of 0.1 radians per minute, how fast is the tip of the shadow moving when the shadow is 20 feet long? This question can be solved by using trigonometry and the chain rule to relate the rates of change of the height of the streetlight and the length of the shadow to the rate of change of the angle of the sun's rays.