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Se sale de un punto en las proximidades de Isla Plana en coordenadas l:37º 34`N L:001º 12`W, navegando sin viento ni corriente a un rumbo verdadero Rv= 220º con velocidad de máquinas 10´. Calcular analíticamente la posición dos horas después (las posiciones están fuera de carta).Departing from a point near Isla Plana at 37º 34' N, 001º 12' W without wind or current on true course Rv = 220º at 10 knots, compute analytically the position 2 hours later:
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Correct answer: c) l: 37º 18.68' N, L: 001º 28.12' W
Why it is correct
In 2 hours at 10 knots the vessel runs d = 20 miles on Rv = 220º (S 40º W): ΔLat = −20 × cos 40º = −15.32′ ⇒ Lat₂ = 37º 34′ N − 15.32′ = 37º 18.68′ N. Departure is A = 20 × sin 40º = 12.86′ W and ΔLong = 12.86 / cos 37º 26′ = 16.19′ W ⇒ Long₂ = 001º 12′ W + 16.12′ W = 001º 28.12′ W.
Why the others are not
- a) Adds the difference of latitude northward instead of subtracting it for a third-quadrant course (220º).
- b) Adds the difference of latitude northward instead of subtracting it for a third-quadrant course (220º).
- d) Adds the difference of latitude northward instead of subtracting it for a third-quadrant course (220º).
How to work it out in the exam
- Find d = 20 miles and ΔLat = −20 · cos 40º = −15.32′ S to get Lat₂ = 37º 18.68′ N.
- Find departure A = 20 · sin 40º = 12.86′ W and ΔLong = A / cos(mean Lat) ≈ 16.1′ W to get Long₂ = 001º 28.12′ W.
Where this question comes from
- Región de Murcia · 2025 · 3ª convocatoria · PY Tipo 1 · question 39 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.