Math Problem Statement

Suppose you're driving down a straight road, a little too fast. There is a police officer positioned 22m off the road who is trying to catch speedsters like yourself. The police officer aims their range finder at your vehicle and the reading indicates that your car is 60 away and that distance is decreasing at a rate of . What is your vehicle's actual speed at that moment? (Your answer should be a positive number.) Give unsimplified final equation

Solution

Let's set up the situation and variables to find your car's actual speed:

Variables

  1. Let:

    • xx be the distance between your car and the point on the road closest to the police officer.
    • y=22my = 22 \, \text{m} be the constant distance between the road and the police officer.
    • ss be the distance between your car and the police officer (the hypotenuse of the triangle formed by xx and yy).
  2. The problem states:

    • s=60ms = 60 \, \text{m} (distance from the police officer to your car at that instant).
    • dsdt=\frac{ds}{dt} = - (the rate at which this distance is decreasing, indicating the officer measures your distance to be getting closer).

Relationships and Goal

Since we want the actual speed of your car along the road, we're interested in dxdt\frac{dx}{dt}, the rate at which xx changes.

Using the Pythagorean theorem, we have: s2=x2+y2s^2 = x^2 + y^2

Step 1: Differentiate with Respect to Time

Differentiating both sides with respect to tt: 2sdsdt=2xdxdt2s \frac{ds}{dt} = 2x \frac{dx}{dt}

Step 2: Solve for dxdt\frac{dx}{dt}

Dividing both sides by 2x2x gives: dxdt=sdsdtx\frac{dx}{dt} = \frac{s \frac{ds}{dt}}{x}

Step 3: Substitute Values

Since y=22y = 22 m and s=60s = 60 m, we can find xx using the Pythagorean theorem: x=s2y2=602222x = \sqrt{s^2 - y^2} = \sqrt{60^2 - 22^2}

Now, plug in these values to get the unsimplified expression for dxdt\frac{dx}{dt}: dxdt=60dsdt602222\frac{dx}{dt} = \frac{60 \cdot \frac{ds}{dt}}{\sqrt{60^2 - 22^2}}

This expression gives the speed of your vehicle along the road.

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Math Problem Analysis

Mathematical Concepts

Related Rates
Pythagorean Theorem
Differentiation

Formulas

s^2 = x^2 + y^2
2s * (ds/dt) = 2x * (dx/dt)
dx/dt = (s * ds/dt) / x

Theorems

Pythagorean Theorem

Suitable Grade Level

Grades 11-12