Assume that the moon takes exactly 30 days to complete the cycle and also assume that it rises in the East exactly at 6.48 p.m. on the first day. On the fourth day, at what time will it rise?

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Q: 128 (IAS/2002)
Assume that the moon takes exactly 30 days to complete the cycle and also assume that it rises in the East exactly at 6.48 p.m. on the first day. On the fourth day, at what time will it rise?

question_subject: 

Logic/Reasoning

question_exam: 

IAS

stats: 

0,1,5,2,1,1,2

keywords: 

{'moon': [2, 0, 5, 2], 'fourth day': [0, 0, 2, 0], 'cycle': [0, 2, 5, 2], 'first day': [0, 0, 2, 0]}

The moon orbits the Earth approximately once every 30 days. This leads to a shift in rising time each day. The moon rises (approximately) 50 minutes later each day because of the combined effect of the Earth`s rotation on its axis and the moon`s orbital motion around Earth. This means that by the fourth day, it will rise around 3*50 minutes after it did on the first day. In calculation, 1 hour and 50 minutes after 6:48 pm is around 9:12 pm.

Option 1 (8:24 pm) and option 3 (10:00 pm) doesn`t fit because the calculations are not close to the 150 minutes shift. Option 4 (11:48 pm) overestimates the delay in the moon`s rise. Thus, option 2 (9.12 pm) is the correct answer as it best fits with the delay calculation.

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