Math Problem Statement

A cyclist travels between point A and point B with a speed represented by the following equation; f'(x)=-3x²+18x What is the maximum speed traveled by the cyclist and what is the distance between the 2 points

Solution

To find the maximum speed of the cyclist represented by the function f(x)=3x2+18xf'(x) = -3x^2 + 18x, we can follow these steps:

  1. Find the critical points: Set the derivative equal to zero to find the critical points. 3x2+18x=0-3x^2 + 18x = 0 Factor out 3x-3x: 3x(x6)=0-3x(x - 6) = 0 This gives us x=0x = 0 and x=6x = 6.

  2. Determine the maximum speed: We evaluate f(x)f'(x) at the critical points and at the endpoints of the domain (if defined). Since no specific interval is given, we consider x=0x = 0 and x=6x = 6: f(0)=3(0)2+18(0)=0f'(0) = -3(0)^2 + 18(0) = 0 f(6)=3(6)2+18(6)=3(36)+108=108+108=0f'(6) = -3(6)^2 + 18(6) = -3(36) + 108 = -108 + 108 = 0

  3. Check the second derivative to confirm maxima: f(x)=6x+18f''(x) = -6x + 18 Evaluate f(6)f''(6): f(6)=6(6)+18=36+18=18(concave down, maximum at x=6)f''(6) = -6(6) + 18 = -36 + 18 = -18 \quad (\text{concave down, maximum at } x=6)

  4. Calculate maximum speed: Since f(0)=0f'(0) = 0 and f(6)=0f'(6) = 0 are both not maximum speeds, we need to confirm the nature of these values: By analyzing values around the critical points, we find that the function increases until x=6x=6 and decreases afterward.

    For practical purposes, if the speed is bounded, xx values should be considered in a defined range, typically from 0 to 6 for practical cycling distances.

  5. Determine the distance traveled: Assuming the speed function represents the cyclist's speed over time, the distance can be calculated using: Distance=06f(x)dx\text{Distance} = \int_{0}^{6} f'(x) \, dx

    Integrate f(x)f'(x): (3x2+18x)dx=x3+9x2+C\int (-3x^2 + 18x) \, dx = -x^3 + 9x^2 + C Evaluating from 00 to 66: [ \left[-x^3 + 9x^2\right]_{0}^{6} = [-(6)^3 + 9(6)^2] - [0] = [-216 + 324] = 108 ]

Thus, the maximum speed traveled by the cyclist is 0 (the maximum speed occurs at endpoints in this context without a defined speed function), and the distance between points A and B is 108 units.

Summary:

  • Maximum Speed: The function's maximum value needs endpoints to assess speed; both evaluated speeds at critical points were zero.
  • Distance: 108 units

Would you like more details on any step? Here are some related questions to consider:

  1. What is the significance of the second derivative in this context?
  2. How would you evaluate speed at different intervals?
  3. Could the function f(x)f'(x) be modified to provide a maximum speed at a different point?
  4. How can you graph this function to visualize the speed?
  5. What implications does this have for the cyclist's performance over different terrains?

Tip: Always check both the critical points and endpoints when dealing with optimization problems in calculus!

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Math Problem Analysis

Mathematical Concepts

Calculus
Optimization
Integration

Formulas

f'(x) = -3x^2 + 18x
Critical points: Set f'(x) = 0
Distance = ∫ f'(x) dx

Theorems

First Derivative Test
Second Derivative Test

Suitable Grade Level

Grades 11-12