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Getting Back. An explorer in the dense jungles of equatorial Africa leaves his hut. He takes 40 steps northeast, then 80 steps \(60^{\circ}\) north of west, then 50 steps due south. Assume his steps all have equal length. (a) Sketch, roughly to scale, the three vectors and their resultant. (b) Save the explorer from becoming hopelessly lost in the jungle by giving him the displacement, calculated using the method of components, that will return him to his hut.

Short Answer

Expert verified
Find the negative of the explorer’s overall displacement vector to determine his return path.

Step by step solution

01

Represent the Vectors Visually

Start by drawing the path the explorer took. Use arrows to represent each segment of the path: 1. First, draw a vector 40 steps long towards the northeast (45° from the north). 2. Next, draw a vector 80 steps long at a 60° angle north of west. 3. Finally, draw a vector 50 steps directly downward (south). These vectors are drawn head-to-tail and their sum is the resultant vector from the starting to the ending point.
02

Resolve the Vectors into Components

Convert each path section into its component vectors. 1. NE: Calculate using 45° as follows - X-component (East): \(40 \cos(45^{\circ})\) - Y-component (North): \(40 \sin(45^{\circ})\)2. 60° N of W: - X-component (West): \(-80 \cos(60^{\circ})\) - Y-component (North): \(80 \sin(60^{\circ})\)3. South: - X-component: 0 - Y-component (South): \(-50\)
03

Calculate the Total Components

Add up the X-components and Y-components separately.- Total X-component: \((40 \cos(45^{\circ})) + (-(80 \cos(60^{\circ}))) + 0\)- Total Y-component: \((40 \sin(45^{\circ})) + (80 \sin(60^{\circ})) + (-50)\)
04

Determine the Resultant Displacement

Using the total X and Y components, find the magnitude of the resultant displacement using the Pythagorean theorem:\[ R = \sqrt{(Total\ X-component)^2 + (Total\ Y-component)^2} \]Determine the angle from the components:\[ \theta = \tan^{-1}\left(\frac{Total\ Y-component}{Total\ X-component}\right) \]
05

Calculate the Displacement to Return to the Hut

The displacement needed to return to the hut is the vector that would bring the starting and endpoint together - essentially, the negative of the resultant vector obtained:1. Reverse the sign of both components: - Return X-component: \(-\text{Total X-component}\) - Return Y-component: \(-\text{Total Y-component}\)From these, calculate the return vector’s magnitude and angle using similar formulas as Step 4.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Displacement
Displacement is the shortest distance between an object's initial and final position, even if the path taken is more complicated. In the context of vector addition, displacement combines direction and magnitude to fully describe movement from one point to another.
In exercises like those involving explorers in the jungle, knowing displacement helps decide how to return to a starting point effectively. Instead of tracing back each step taken, displacement directly tells us how far and what direction to move to return to the origin.
Understanding displacement allows you to appreciate how vector paths can be simplified to a single, straightforward movement, saving time and effort.
Vector Components
When dealing with vectors, it's often useful to break them down into vector components in a rectangular coordinate system. This means separating a vector into its horizontal (x-axis) and vertical (y-axis) components.
In our exercise, the explorer's movements in northeast, north of west, and southern directions can be translated into x (east-west) and y (north-south) components. For each vector, trigonometric functions are used to calculate these components:
  • Use cosine for the x-component of a vector, as it corresponds to the adjacent side in a right triangle.

  • Use sine for the y-component, representing the opposite side.
By breaking down vectors this way, it becomes easier to analyze and combine them mathematically.
Pythagorean Theorem
The Pythagorean theorem is a fundamental part of vector addition. This mathematical principle relates the square of the hypotenuse of a right-angled triangle to the squares of its other two sides.
Once you have calculated the total x and y components from various paths, the Pythagorean theorem can be used to find the resultant vector's magnitude.
The equation to remember is:
\[ R = \sqrt{(Total\ X-component)^2 + (Total\ Y-component)^2} \]This resultant vector represents the total displacement from the explorer's initial position to where they currently are. Understanding how the Pythagorean theorem fits into vector mathematics is essential for calculating precise movements in physics and real-world situations.
Vector Resolution
Vector resolution is the process of breaking down a vector into its components, essentially the reverse of vector addition. By resolving vectors, we arrange them in simpler parts that can be easily analyzed and calculated.
In practical scenarios like returning to a starting point in the jungle, vector resolution helps in determining the exact path one needs to take back. Simply calculate the negative of the final resultant vector's components—just reverse the signs—and you'll have the displacement vector required to return.
From there, determining the exact magnitude and direction for the return path becomes straightforward:
  • Reverse the signs of the x and y components.

  • Calculate the resultant's magnitude and angle using the same methods as for initial displacement.
Mastering vector resolution allows for more accurate and efficient navigation by intelligently using diagonal or complex paths.

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Most popular questions from this chapter

With a wooden ruler you measure the length of a rectangular piece of sheet metal to be 12 \(\mathrm{mm} .\) You use micrometer calipers to measure the width of the rectangle and obtain the value 5.98 \(\mathrm{mm} .\) Give your answers to the following questions to the correct number of significant figures. (a) What is the area of the rectangle? (b) What is the ratio of the rectangle's width to its length? (c) What is the perimeter of the rectangle? (d) What is the difference between the length and width? (e) What is the ratio of the length to the width?

You are camping with two friends, Joe and Karl. Since all three of you like your privacy, you don't pitch your tents close together. Joe's tent is 21.0 \(\mathrm{m}\) from yours, in the direction \(23.0^{\circ}\) south of east. Karl's tent is 32.0 \(\mathrm{m}\) from yours, in the direction \(37.0^{\circ}\) north of east. What is the distance between Karl's tent and Joe's tent?

Two workers pull horizontally on a heavy box, but one pulls twice as hard as the other. The larger pull is directed at \(25.0^{\circ}\) west of north, and the resultant of these two pulls is 460.0 \(\mathrm{N}\) directly northward. Use vector components to find the magnitude of each of these pulls and the direction of the smaller pull.

Hearing rattles from a snake, you make two rapid displacements of magnitude 1.8 \(\mathrm{m}\) and 2.4 \(\mathrm{m} .\) In sketches (roughly to scale), show how your two displacements might add up to give a resultant of magnitude (a) \(4.2 \mathrm{m} ;\) (b) \(0.6 \mathrm{m} ;\) (c) 3.0 \(\mathrm{m} .\)

Find the magnitude and direction of the vector represented by the following pairs of components: (a) \(A_{x}=-8.60 \mathrm{cm}$$A_{y}=5.20 \mathrm{cm} ;\) (b) \(A_{x}=-9.70 \mathrm{m}, \quad A_{y}=-2.45 \mathrm{m} ;\) (c) \(A_{x}=\) \(7.75 \mathrm{km}, A_{y}=-2.70 \mathrm{km}\)

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