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Difficulty: MediumLocation, Size, and Political Divisions of Africa

The easternmost point of the African mainland, Ras Hafun in Somalia, is located at approximately longitude 51∘E51^\circ\text{E}, while the westernmost point, Pointe des Almadies in Senegal, lies at approximately 17∘W17^\circ\text{W}. If the local solar time at Pointe des Almadies is 8:00 AM, what is the local solar time at Ras Hafun?

  1. 12:32 PMAnswer
  2. B
    3:28 AM
  3. C
    10:16 AM
  4. D
    5:44 AM

Answer

12:32 PM
The total longitudinal interval spanning between 17∘W17^\circ\text{W} (Senegal) and 51∘E51^\circ\text{E} (Somalia) is 68∘68^\circ. At 4 minutes per degree of longitude, this equals a 272-minute difference, or 4 hours and 32 minutes. Because Somalia is situated east of Senegal, time is added to 8:00 AM, arriving at 12:32 PM.

Step-by-Step Solution

1
Calculate the total longitudinal separation between the two points across the Prime Meridian.
51∘E−(−17∘W)=51∘+17∘=68∘51^\circ\text{E} - (-17^\circ\text{W}) = 51^\circ + 17^\circ = 68^\circ
Because one point is in the Eastern Hemisphere and the other is in the Western Hemisphere, their longitudinal values must be added to find the total distance in degrees.
2
Convert the longitudinal difference into a time difference.
68∘×4 minutes/degree=272 minutes=4 hours and 32 minutes68^\circ \times 4\text{ minutes/degree} = 272\text{ minutes} = 4\text{ hours and } 32\text{ minutes}
The Earth rotates 360∘360^\circ in 24 hours, which equals 1∘1^\circ every 4 minutes.
3
Adjust the time based on direction of travel relative to the reference point.
8:00 AM+4 hours 32 minutes=12:32 PM8:00\text{ AM} + 4\text{ hours } 32\text{ minutes} = 12:32\text{ PM}
Places located farther east experience sunrise earlier, so time is added when moving east.

Key Concept

Longitudinal extent of Africa and time calculations across the Prime Meridian
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Topics

Location, Size, and Political Divisions of Africa

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