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A ship travels 100 km on a bearing of 045°, then turns to a bearing of 120° and travels 180 km to its destination. (i) Sketch the path travelled by the ship. (ii) Find the distance of ship from its original position. (iii) Find the bearing from the original position.

Mathematics

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Answers

2 parts
ii

227.41 km\text{227.41 km}

iii

094.9∘094.9^\circ

Step-by-step solution

5 steps

Part i· 1 step

  1. Sketch the path.

    • Start at the origin, O. Draw a North line.
    • From O, draw a line segment OA, representing 100 km, at an angle of 045∘045^\circ clockwise from the North line.
    • At point A, draw another North line.
    • From A, draw a line segment AB, representing 180 km, at an angle of 120∘120^\circ clockwise from the North line at A.
    • Point B is the destination. The path is O to A, then A to B.

Part ii

227.41 km\text{227.41 km}

  1. Determine the interior angle ∠OAB\angle OAB.

    The North line at O and the North line at A are parallel. The line OA is a transversal.
    The angle between the North line at A and the line AO (pointing towards O) is 45∘45^\circ (alternate interior angle to the 045∘045^\circ bearing).
    The angle from the North line at A, clockwise to AB is 120∘120^\circ.
    The angle from the North line at A, clockwise to the South line at A is 180∘180^\circ.
    So, the angle from the South line at A, counter-clockwise to AB is 180∘−120∘=60∘180^\circ - 120^\circ = 60^\circ.
    Therefore, ∠OAB=45∘+60∘=105∘\angle OAB = 45^\circ + 60^\circ = 105^\circ.

  2. Apply the Cosine Rule to find the distance OB.

    Using the Cosine Rule in △OAB\triangle OAB:

    OB2=OA2+AB2−2(OA)(AB)cos⁡(∠OAB)OB^2 = OA^2 + AB^2 - 2(OA)(AB)\cos(\angle OAB)

    Substitute the given values: OA=100OA = 100 km, AB=180AB = 180 km, ∠OAB=105∘\angle OAB = 105^\circ.

    OB2=1002+1802−2(100)(180)cos⁡(105∘)OB^2 = 100^2 + 180^2 - 2(100)(180)\cos(105^\circ) OB2=10000+32400−36000(−0.258819)OB^2 = 10000 + 32400 - 36000(-0.258819) OB2=42400+9317.484OB^2 = 42400 + 9317.484 OB2=51717.484OB^2 = 51717.484 OB=51717.484OB = \sqrt{51717.484} OB≈227.41 kmOB \approx 227.41 \text{ km}

    The distance of the ship from its original position is 227.41 km\boxed{\text{227.41 km}}.

Part iii

094.9∘094.9^\circ

  1. Apply the Sine Rule to find ∠AOB\angle AOB.

    Using the Sine Rule in △OAB\triangle OAB:

    sin⁡(∠AOB)AB=sin⁡(∠OAB)OB\frac{\sin(\angle AOB)}{AB} = \frac{\sin(\angle OAB)}{OB} sin⁡(∠AOB)=ABsin⁡(∠OAB)OB\sin(\angle AOB) = \frac{AB \sin(\angle OAB)}{OB}

    Substitute the values: AB=180AB = 180 km, ∠OAB=105∘\angle OAB = 105^\circ, OB=227.4148OB = 227.4148 km.

    sin⁡(∠AOB)=180sin⁡(105∘)227.4148\sin(\angle AOB) = \frac{180 \sin(105^\circ)}{227.4148} sin⁡(∠AOB)=180×0.9659258227.4148\sin(\angle AOB) = \frac{180 \times 0.9659258}{227.4148} sin⁡(∠AOB)≈0.76453\sin(\angle AOB) \approx 0.76453 ∠AOB=arcsin⁡(0.76453)\angle AOB = \arcsin(0.76453) ∠AOB≈49.86∘\angle AOB \approx 49.86^\circ
  2. Calculate the bearing from the original position.

    The bearing of B from O is the initial bearing of A from O plus ∠AOB\angle AOB.
    Bearing =045∘+∠AOB= 045^\circ + \angle AOB
    Bearing =45∘+49.86∘= 45^\circ + 49.86^\circ
    Bearing =94.86∘= 94.86^\circ
    Rounded to one decimal place, the bearing is 094.9∘\boxed{094.9^\circ}.

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