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Question 46 PPL page 392
leminhphuong
Topic Author
leminhphuong created the topic: Question 46 PPL page 392
Dear Bob,
Can you please explain why the correct answer for above question is A (11 hours 25 minutes) ?. I do not really understand . My answer is D
Thanks
Richard replied the topic: Question 46 PPL page 392
G'day,
BOD in Hay occurs at 0615 LMT (Local Meant Time). LMT is a time specific to the meridian of longitude where Hay is situated, so in order to compare it with a time from another meridian (such as Ayers Rock in the example), we need to convert it to some common standard. This standarad time is called UTC.
Hay is 144 degrees 50 minutes East, which (using the arc to time table) is 9hr 39min ahead of UTC. The time of BOD in Hay expressed in UTC is therefore 9hr 39min earlier. Subtracting 09:39 from 0615 LMT gives you 20:36 UTC, the day before.
We use the same strategy to convert the EOD in Ayers Rock to UTC. EOD there occurs at 1715 LMT but Ayers is 130 degrees 59 minutes East. Using the arc to time table we find this equates to a time difference of 8hr 44min between Ayers Rock and Greenwich. Therefore, when it is EOD in Ayers Rock, the UTC time is 8hr 44 minutes earlier. 1715 LMT minue 8hr 44min is 0831 UTC.
To find the hours of daylight between the two times, subtract BOD from EOD:
0831 UTC (EOD) - 2036 UTC BOD) = 11hr 55min difference.
We want to arrive 30 minutes before last light so the actual daylight available to us is 30 minutes less than that. 11hr 55minutes - 30minutes = 11 hr 25 minutes. Answer (A).
. My answer is D