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El 28 de Abril de 2024 el yate PUNTA PRIMA zarpa de las proximidades del puerto de La Savina en coordenadas l:38º 44`N L:001º 24`E navegando al Rumbo verdadero 310º con velocidad de máquinas 10 nudos durante 2 horas no afectado por viento ni corriente, corrección total= - 5º. Calcular Posición del buque 2 horas después y Rumbo de aguja.On 28 April 2024 the yacht PUNTA PRIMA departs from 38º 44' N, 001º 24' E on true course 310º at 10 knots for 2 hours without wind or current (Ct = −5º). What are her position after 2 hours and her compass course?
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Correct answer: c) l = 38º 56.8' N, L = 001º 04.4' E, Ra = 315º
Why it is correct
In 2 h at 10 knots she covers d = 20 miles on Rv = 310º (N 50º W): ΔLat = 20 × cos 50º = +12.86′ N ⇒ Lat₂ = 38º 56.8′ N; departure A = 20 × sin 50º = 15.32′ W and ΔLong = 15.32 / cos 38º 50.4′ = 19.67′ W ⇒ Long₂ = 001º 24′ E − 19.6′ = 001º 04.4′ E. Also, Ra = Rv − Ct = 310º − (−5º) = 315º.
Why the others are not
- a) Does not match ΔLat = +12.9′ N, ΔLong = −19.6′ W and Ra = Rv − Ct = 315º.
- b) Does not match ΔLat = +12.9′ N, ΔLong = −19.6′ W and Ra = Rv − Ct = 315º.
- d) Does not match ΔLat = +12.9′ N, ΔLong = −19.6′ W and Ra = Rv − Ct = 315º.
How to work it out in the exam
- Find Ra = Rv − Ct = 310º − (−5º) = 315º and distance d = 10 × 2 = 20 miles.
- Compute ΔLat = 20 · cos 50º = +12.86′ N and ΔLong = (20 · sin 50º) / cos(mean Lat) = −19.67′ W.
Where this question comes from
- Región de Murcia · 2024 · 3ª convocatoria · PY Tipo 1 · question 39 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.