Math Problem Statement

An elastic rope is attached to the ground at the positions shown in the picture. The rope is being pulled up along the dotted line. Assume the units are meters. Assume that x is increasing at a rate of 5 meters/sec. (a) Write θ as a function of x. (b) When x=10, the angle θ is changing at a rate of ___ rad/sec. (c) Let L be the left hand piece of rope and R the right hand piece of rope. When x=10, is the rate of change of L larger than the rate of change of R?

Solution

To tackle this problem, let's break it down into parts based on the given information and questions:

Given Information

  • The horizontal distances in the setup are 99 meters to the left and 33 meters to the right from the center where the rope is being pulled.
  • xx represents the vertical distance from the ground level to the point where the rope is pulled up.
  • The rate of change of xx with respect to time dxdt=5\frac{dx}{dt} = 5 meters per second.

Questions

Part (a)

Write θ\theta as a function of xx.

The angle θ\theta is formed at the left attachment point of the rope. Using trigonometry:

  • The distance opposite θ\theta is xx.
  • The horizontal distance adjacent to θ\theta is 99.

Thus, we can express θ\theta in terms of xx as: θ=arctan(x9)\theta = \arctan\left(\frac{x}{9}\right)

Part (b)

When x=10x = 10, find the rate at which θ\theta is changing, i.e., dθdt\frac{d\theta}{dt}.

To find dθdt\frac{d\theta}{dt}, we differentiate θ=arctan(x9)\theta = \arctan\left(\frac{x}{9}\right) with respect to time tt: dθdt=11+(x9)219dxdt\frac{d\theta}{dt} = \frac{1}{1 + \left(\frac{x}{9}\right)^2} \cdot \frac{1}{9} \cdot \frac{dx}{dt}

Plugging in dxdt=5\frac{dx}{dt} = 5 and x=10x = 10:

  1. Substitute x=10x = 10 into the expression inside the square term: dθdt=11+(109)2195\frac{d\theta}{dt} = \frac{1}{1 + \left(\frac{10}{9}\right)^2} \cdot \frac{1}{9} \cdot 5
  2. Simplify this expression to get the value of dθdt\frac{d\theta}{dt}.

Part (c)

Compare the rate of change of the left-hand piece of the rope (L) with the right-hand piece of the rope (R) when x=10x = 10.

To determine if the rate of change of LL is greater than that of RR, we can examine the distances:

  1. The left side LL is longer than the right side RR (since the left side horizontal component is 99 meters and the right side is 33 meters).
  2. Given that xx is increasing, the left side LL will experience a greater rate of change compared to RR because of the larger horizontal base.

Therefore, Yes, the rate of change of LL will be larger than that of RR when x=10x = 10.

Would you like further details on any specific part of the solution?


Here are 5 related questions for further exploration:

  1. How would the result change if xx were increasing at a different rate?
  2. What if the horizontal distances on either side of the pulling point were equal?
  3. How does the angle θ\theta behave as xx approaches zero?
  4. How would we calculate the total length of rope needed for different values of xx?
  5. How would the rate of change of θ\theta be affected if the distances on either side were reversed?

Tip: When working with related rates, carefully identify the relationships and differentiate with respect to time for accurate results.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Related Rates
Differentiation

Formulas

θ = arctan(x / 9)
dθ/dt = (1 / (1 + (x / 9)^2)) * (1 / 9) * dx/dt

Theorems

Chain Rule for Differentiation
Trigonometric Functions

Suitable Grade Level

Grades 11-12