A surveyor leaves her base camp and drives 42km on a bearing of 032⁰ . She then drives 28km on a bearing of 154⁰, how far is she then from her base camp and what is her bearing from it ?

Chemistry

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Answer

AC=36.1 kmAC = 36.1 \text{ km}

Bearing=073∘\text{Bearing} = 073^\circ

Step-by-step solution

3 steps

To solve this navigation problem, we will use trigonometry, specifically the Cosine Rule and the Sine Rule, after sketching the path taken by the surveyor.

  1. Sketch the diagram and determine the interior angle of the triangle.

    Let the base camp be point A.
    The surveyor drives 42 km on a bearing of 032∘032^\circ to point B.
    From point B, she drives 28 km on a bearing of 154∘154^\circ to point C.
    We need to find the distance AC and the bearing of C from A.

    First, let's find the interior angle ∠ABC\angle ABC.
    Draw a North line at B.
    The line BA (from B to A) is on a back bearing from the first leg. The bearing of AB is 032∘032^\circ. The angle from the North line at B, measured clockwise to BA, is 032∘+180∘=212∘032^\circ + 180^\circ = 212^\circ.
    The line BC (from B to C) is on a bearing of 154∘154^\circ. This is the angle from the North line at B, measured clockwise to BC.
    The interior angle ∠ABC\angle ABC is the difference between these two angles:

    ∠ABC=212∘−154∘=58∘\angle ABC = 212^\circ - 154^\circ = 58^\circ
  2. Calculate the distance from the base camp (AC) using the Cosine Rule.

    In △ABC\triangle ABC:
    AB=42AB = 42 km
    BC=28BC = 28 km
    ∠ABC=58∘\angle ABC = 58^\circ
    Using the Cosine Rule: AC2=AB2+BC2−2(AB)(BC)cos⁡(∠ABC)AC^2 = AB^2 + BC^2 - 2(AB)(BC) \cos(\angle ABC)

    AC2=422+282−2(42)(28)cos⁡(58∘)AC^2 = 42^2 + 28^2 - 2(42)(28) \cos(58^\circ) AC2=1764+784−2352cos⁡(58∘)AC^2 = 1764 + 784 - 2352 \cos(58^\circ) AC2=2548−2352(0.529919...)AC^2 = 2548 - 2352(0.529919...) AC2=2548−1246.307AC^2 = 2548 - 1246.307 AC2=1301.693AC^2 = 1301.693 AC=1301.693AC = \sqrt{1301.693} AC≈36.079 kmAC \approx 36.079 \text{ km}

    Rounding to one decimal place:

    AC=36.1 km\boxed{AC = 36.1 \text{ km}}
  3. Calculate the bearing from the base camp (bearing of C from A) using the Sine Rule.

    To find the bearing of C from A, we need to find the angle ∠BAC\angle BAC and add it to the initial bearing of AB (032∘032^\circ).
    Using the Sine Rule in △ABC\triangle ABC: sin⁡(∠BAC)BC=sin⁡(∠ABC)AC\frac{\sin(\angle BAC)}{BC} = \frac{\sin(\angle ABC)}{AC}

    sin⁡(∠BAC)28=sin⁡(58∘)36.079\frac{\sin(\angle BAC)}{28} = \frac{\sin(58^\circ)}{36.079} sin⁡(∠BAC)=28×sin⁡(58∘)36.079\sin(\angle BAC) = \frac{28 \times \sin(58^\circ)}{36.079} sin⁡(∠BAC)=28×0.84804836.079\sin(\angle BAC) = \frac{28 \times 0.848048}{36.079} sin⁡(∠BAC)=23.74534436.079\sin(\angle BAC) = \frac{23.745344}{36.079} sin⁡(∠BAC)≈0.65800\sin(\angle BAC) \approx 0.65800 ∠BAC=arcsin⁡(0.65800)\angle BAC = \arcsin(0.65800) ∠BAC≈41.15∘\angle BAC \approx 41.15^\circ

    The bearing of C from A is the bearing of AB plus ∠BAC\angle BAC:

    Bearing=032∘+41.15∘\text{Bearing} = 032^\circ + 41.15^\circ Bearing=73.15∘\text{Bearing} = 73.15^\circ

    Rounding to the nearest degree and expressing as a three-figure bearing:

    Bearing=073∘\boxed{\text{Bearing} = 073^\circ}
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