You will be hiking to a lake with some of your friends by following the trails indicated on a map at the trailhead. The map says that you will travel 4.00 mi directly north, then 5.31 mi in a direction 35.0° east of north, then finally 1.10 mi in a direction 15.0° north of east. Assume north to be +y and east to be +x. Find the direction of the displacement vector for the hike. Enter the answer as an angle north of east.

Respuesta :

Answer:[tex]\theta =64.58^{\circ}[/tex]

Explanation:

Given

First you travel 4 mi North

position vector [tex]\vec{r_1}[/tex] for this displacement is given by

[tex]\vec{r_1}=4\hat{j}[/tex]

Now you travel 5.31 mi [tex]35^{\circ} east of North; Position vector [tex]\vec{r_2}[/tex] w.r.t [tex]r_1[/tex] is given by

[tex]\vec{r_{21}}=5.31(\sin(35)\hat{i}+\cos(35)\hat{j})[/tex]

Now you travel 1.1 mi in a direction [tex]15^{\circ}[/tex] North of east; Position vector [tex]\vec{r_3}[/tex] w.r.t [tex]r_2[/tex] is given by

[tex]\vec{r_{32}}=1.10(\sin(15)\hat{j}+\cos(15)\hat{i})[/tex]

Thus Position Vector of [tex]r_3[/tex] w.r.t starting Point

[tex]\vec{r_3}=\vec{r_{32}}+\vec{r_{21}}+\vec{r_1}[/tex][tex]\vec{r_3}=4\hat{j}+5.31(\sin(35)\hat{i}+\cos(35)\hat{j})+1.10(\sin(15)\hat{j}+\cos(15)\hat{i})[/tex]

[tex]\vec{r_3}=\hat{i}\left [ 5.31\sin 35+1.1\cos15\right ]+\hat{j}\left [ 4+5.31\cos 35+1.1\sin15\right ][/tex]

[tex]\vec{r_3}=4.10\hat{i}+8.63\hat{j}[/tex]

For angle

[tex]\tan \theta =\frac{8.63}{4.10}[/tex]

[tex]\tan \theta =2.10[/tex]

[tex]\theta =64.58^{\circ}\ North\ of\ east[/tex]

The magnitude of the hiker's displacement is 6.4 mi in a direction of  8.3⁰ north of east.

A sketch of the hiker's displacement

The sketch of the hiker's displacement will form a triangle and the resultant displacement of the triangle will be opposite to the largest angle of the triangle.

The largest angle of the triangle = 90 + 65 + 15 = 170⁰

Magnitude of the resulatant displacement

Apply Parallellogram law of vector addition

R² = a² + b² - 2bc(cosθ)

R² = (5.31)² + (1.1)² - 2(5.31)(1.1)cos(170)

R² = 40.9

R = √40.9

R = 6.4 mi

Direction of the displacement

Apply sine rule

R/sin170 = 5.31/sinθ

6.4/sin(170) = 5.31/sinθ

36.856 = 5.31/sinθ

sinθ = 5.31/36.856

sinθ =  0.144

θ = sin⁻¹(0.144)

θ = 8.3⁰

Thus, the magnitude of the hiker's displacement is 6.4 mi in a direction of  8.3⁰ north of east.

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