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Ship Ladder


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#1 rookie1ja

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Posted 30 March 2007 - 03:27 PM

Ship Ladder - Back to the Logic Puzzles
A ladder hangs over the side of a ship anchored in a port. The bottom rung touches the water. The distance between rungs is 20 cm and the length of the ladder is 180 cm. The tide is rising at the rate of 15 cm each hour.
When will the water reach the seventh rung from the top?

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#2 normdeplume

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Posted 13 June 2007 - 05:28 PM

This rather depends on the tension on the Anchor, If the Ship is Anchored with no slack then it can not rise with the tide, and in this instance it would take 10 hours and 40 minutes to reach the 8 rung (third from the top).

Only if there is enough slack to allow a full 180cm rise in the tide could you answer be correct.
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#3 larryhl

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Posted 14 June 2007 - 01:31 PM

This rather depends on the tension on the Anchor, If the Ship is Anchored with no slack then it can not rise with the tide, and in this instance it would take 10 hours and 40 minutes to reach the 8 rung (third from the top).

Only if there is enough slack to allow a full 180cm rise in the tide could you answer be correct.



I have yet to know any decent seaman anchor a ship without allowing for tide...
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#4 sharknateher

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Posted 14 June 2007 - 07:04 PM

Ok first of all you got me. And so the math I did is irrelevant, but since others worked it out too, I am confused as to how you got to the answer of 10 hours 40 minutes to reach the 8th stave. As I did the math, the ladder is 180 cm long and the distance between staves is 20 cm. 180 / 20 = 9 staves. So if we are trying to get the the third from the top our target stave would be number seven not number eight.

If the above math is correct then the target height is 120 cm (remeber the number 1 stave is at 0 cm not at 20 cm)

If the target height is 120 cm and the tide rises at 15 cm per hour then it would take eight hours to reach the number seven stave (120/15).

Just assume the tide rises and the boat doesn't is my math faulty?
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#5 normdeplume

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Posted 18 June 2007 - 09:32 AM

Sharkmateher - Your math is wrong, as you mention the bottom stave is zero so to get to 180 you need 10 staves not 9 (see below)

180 --- 10
160 --- 9
140 --- 8
120 --- 7
100 --- 6
80 --- 5
60 --- 4
40 --- 3
20 --- 2
0 --- 1

Larryhl. I was playing devil's advocate, nowhere in the puzzle does it say that the ship is anchored by a good saeman! But I agree it is likely to have enough slack, for the original answer to be correct.
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#6 mmagied

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Posted 26 June 2007 - 09:43 PM

My initial thoughts was that it depends on
-how far in the tide is already
-where the boat is docked
-what phase the moon is in
...since the degree of the change of tide changes dramatically with location and time of year.

But of course this doesn't matter based on the answer...just thought it would be something else to think about:)
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#7 beaker_reborn

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Posted 06 July 2007 - 10:18 PM

When the ship sinks.
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#8 davheili

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Posted 12 July 2007 - 09:44 PM

Given that an anchor prevents a ship from moving by dragging through the mud, and not by physically attaching the ship to the bottom of the harbor; And given that most ships have no problem floating with their anchor(s) on deck; I propose that the ship would simply rise with the tide pulling the anchor off the bottom of the harbor when the slack runs out. So it doesn't really matter if there is slack in the anchor chain or not.
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#9 wrzesinski

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Posted 15 July 2007 - 01:03 AM

NEVER...the boat wouldn't have an anchor heavy enough to hold it in place with the raising tide or the boat wouldn't be able to float with the anchor up...
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#10 Riddari

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Posted 24 July 2007 - 05:44 PM

I agree with the answer as given. However, since the boat is in port, it could be empty at the time the bottom tave is touching the water, which would make a certain amount of sense. As the ship is loaded, it could sink down to the point that the third tave from the top is touching the water. Of course, there is not enough information given to properly answer the question more precisely that saying "when it is loaded".
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