Math Problem Statement

A man wandering in the desert walks 5.7 miles in the direction S 26 degrees W. He then turns 90 degrees and walks 9 miles in the direction N  W. At that time, how far is he from his starting point, and what is his bearing from his starting point?

Solution

We can solve this problem using vector analysis and trigonometry. The man walks in two legs, and we need to determine his distance from the starting point (which will form a triangle) and his final bearing.

Step 1: Breakdown of the directions

  • First, the man walks 5.7 miles in the direction S 26° W. This means the angle is 26 degrees west of the south.
  • Then, he turns 90° and walks 9 miles in the direction N W, which means 45 degrees west of north.

We want to determine:

  1. The straight-line distance from his final position back to his starting point (i.e., the hypotenuse of a triangle).
  2. His bearing from the starting point.

Step 2: Decompose the walks into components

We'll break each leg of his walk into its north-south (vertical) and east-west (horizontal) components using trigonometry.

Leg 1: 5.7 miles at S 26° W

  • Southward component: 5.7×cos(26)5.7 \times \cos(26^\circ)
  • Westward component: 5.7×sin(26)5.7 \times \sin(26^\circ)

Calculating: Southward component=5.7×cos(26)5.7×0.8988=5.122 miles south\text{Southward component} = 5.7 \times \cos(26^\circ) \approx 5.7 \times 0.8988 = 5.122 \text{ miles south} Westward component=5.7×sin(26)5.7×0.4384=2.500 miles west\text{Westward component} = 5.7 \times \sin(26^\circ) \approx 5.7 \times 0.4384 = 2.500 \text{ miles west}

Leg 2: 9 miles at N W (45 degrees west of north)

  • Northward component: 9×cos(45)9 \times \cos(45^\circ)
  • Westward component: 9×sin(45)9 \times \sin(45^\circ)

Since cos(45)=sin(45)0.7071\cos(45^\circ) = \sin(45^\circ) \approx 0.7071, we can calculate:

Northward component=9×0.7071=6.364 miles north\text{Northward component} = 9 \times 0.7071 = 6.364 \text{ miles north} Westward component=9×0.7071=6.364 miles west\text{Westward component} = 9 \times 0.7071 = 6.364 \text{ miles west}

Step 3: Total displacement in the north-south and east-west directions

Now we sum the north-south and east-west components.

  • North-south direction:

    • He walked 5.122 miles south in the first leg and 6.364 miles north in the second leg.
    • Net displacement: 6.3645.122=1.242 miles north6.364 - 5.122 = 1.242 \text{ miles north}
  • East-west direction:

    • He walked 2.500 miles west in the first leg and 6.364 miles west in the second leg.
    • Net displacement: 2.500+6.364=8.864 miles west2.500 + 6.364 = 8.864 \text{ miles west}

Step 4: Calculate the straight-line distance (resultant vector)

The man's straight-line distance from his starting point is the hypotenuse of the right triangle formed by the north-south and east-west displacements. Use the Pythagorean theorem:

d=(1.242)2+(8.864)2d = \sqrt{(1.242)^2 + (8.864)^2}

Calculating:

d=1.542+78.573=80.1158.951 milesd = \sqrt{1.542 + 78.573} = \sqrt{80.115} \approx 8.951 \text{ miles}

Step 5: Determine the bearing

The bearing

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Vector Analysis
Right Triangle Geometry

Formulas

Southward component: distance * cos(angle)
Westward component: distance * sin(angle)
Pythagorean theorem: d = √(north-south displacement² + east-west displacement²)
Bearing angle: arctan(westward displacement / northward displacement)

Theorems

Pythagorean Theorem
Basic Trigonometry

Suitable Grade Level

Grades 9-12