Chapter 3: Problem 35
A hot-air balloon is \(150 \mathrm{ft}\) above the ground when a motorcycle passes directly beneath it (traveling in a straight line on a horizontal road) going \(40 \mathrm{mi} / \mathrm{hr}(58.67 \mathrm{ft} / \mathrm{s})\) If the balloon is rising vertically at a rate of \(10 \mathrm{ft} / \mathrm{s},\) what is the rate of change of the distance between the motorcycle and the balloon 10 seconds later?
Short Answer
Step by step solution
Set up a coordinate system and label variables
Write equations for \(x(t)\), \(y(t)\), and \(z(t)\)
Differentiate the equation with respect to time
Evaluate the desired rate 10 seconds later
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Pythagorean Theorem
- \(a^2 + b^2 = c^2\)
- We compute \(z(t)^2 = x(t)^2 + y(t)^2\)
- This sets the stage to apply differentiation to find related rates.
Differentiation
- \(\frac{d}{dt}[x(t)]\)
- \(\frac{d}{dt}[y(t)]\)
- \(\frac{d}{dt}[z(t)]\)
In our equation: \[2z(t) \cdot \frac{d}{dt}[z(t)] = 2x(t) \cdot \frac{d}{dt}[x(t)] + 2y(t) \cdot \frac{d}{dt}[y(t)]\]the derivatives translate into actionable insights for determining unknown rates.
Coordinate System
- The motorcycle starts at the origin \((0,0)\), moving in the positive x-direction.
- The balloon starts 150 ft above ground, moving in the positive y-direction.
- \(x(t)\) represents the horizontal motion of the motorcycle.
- \(y(t)\) stands for the vertical rise of the balloon.
Rate of Change
- The horizontal speed of the motorcycle: 58.67 ft/s.
- The ascent rate of the balloon: 10 ft/s.
- Applying the Pythagorean theorem to determine \(z(t)\) at a specific moment.
- Employing differentiation to compute how \(z(t)\) evolves as \(x(t)\) and \(y(t)\) proceed independently.