Question

A power failure on the bridge of a Great Lakes freighter has resulted in the ship's navigator having to do her own calculations. She measures the angle between the ship's course and a lighthouse on shore as 32°. After the ship has travelled 1500 m, she measures the angle to be 72°. Determine if the ship was closer to or farther from the lighthouse at the second sighting, and by what distance. (4 marks)

It is impossible to measure the length of a particular swamp directly. Kendra put a stake in the ground and measured from the stake to opposite ends of the swamp, the results being 410 m and 805 m. She measured the angle between the distances to be 57°. What is the length of the swamp? (4 marks)

Answer 1

1) The ship is closer

2) 675.73 m

Explanation:

1) The given parameters are;

The initial angle between the ship's course and the lighthouse = 32°

The final angle between the ship's course and the lighthouse = 72°

The distance traveled by the sip between he two positions = 1500 m

Therefore we have a triangle formed between the distance covered by the ship and the two distances of the ship from the lighthouse, a and b

Where;

a = The initial distance fro the lighthouse

b = The final distance fro the lighthouse

The angles of the triangle are

32°, (180 - 72) = 108° and 180 - 32 - 108 = 40°

By sine rule we have;

1500/(sin(40)) = a/(sin(108)) = b/(sin(32)) =

Therefore, a = sin(108°) × 1500/(sin(40°)) = 2219.37 m

b = (sin(32°)) × 1500/(sin(40°)) = 1236.61 m

Therefore, a > b

The initial distance fro the lighthouse > The final distance fro the lighthouse, which shows that the ship is closer

2) By cosine rule we have

a² = b² + c² - 2× b×c×cos(A)

Where the given measurements by Kendra are;

410 m and 805 m with an included (in between) angle of 57°, we have;

Let b = 410 m, c = 805 m, and A = 57°, we have;

a² = 410^2 + 805^2 - 2× 410×805×cos(57 degrees) = 456608.77 m²

a = The length of the stream = 675.73 m.