You land your inflatable boat on a sandbar at high tide in Southeast Alaska, which has a large semi- diurnal tide. You intend to be away from the boat for 12 hours, but come back early after only 8 hours. Your boat is, unfortunately, 400m from shore. How long will you have to wait to be able to use your boat assuming you can't carry it.?
A) 6 hours
B) 12 hours and 25 minutes
C) 4 hours and 25 minutes
D) 6 hours and 12 minutes

Question

Quizplus · Accepted Answer

Southeast Alaska has a large semi-diurnal tide, which means there are two high tides and two low tides every day, and the differences between them are generally consistent. If the boat was landed at high tide, it would have been floating when the tide was at its highest level. The tide would then begin to go out, and after 8 hours, it would be partly out. If the tide were truly halfway out, you would know you'd have about half the time you were gone left before the boat would be back in the water. If the tide was almost all the way out, you might guess that it'd be twice as long until it came back in.

Therefore, the best choice is (C) 4 hours and 25 minutes, which is half of the original 8.5-hour tidal period (high tide to the next high tide) for Southeast Alaska (the difference between high and low tide is not given, so we use the average tidal period as a reference).

You Land Your Inflatable Boat on a Sandbar at High