# Logic Problem **URL:** \ **Category:** Factual Questions\ **Created:** [May 15, 2003, 7:19pm UTC](https://boards.straightdope.com/t/logic-problem/175515 "2003-05-15T19:19:00Z")\ **Posts on this page:** 14\ **Page:** 3
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [May 18, 2003, 6:37pm UTC](https://boards.straightdope.com/t/logic-problem/175515/41 "2003-05-18T18:37:44Z")
1. Let’s use Shade’s method of looping the ditch with a noose knot and pulling it tight, then going over the pole, lowering yourself into the ditch at the other side of the planet and anchoring it. 2. Then keep going back to the pole and dropping longitudinal threads and anchoring them in the ditch. (Only climb back up fully anchored ropes.) 3. Then create a network of latitudinal threads and knot them at the intersections. Keep this up even going down the side of the ditch. 4. Now, you can’t tie off a loop at the other side of the bottom of the ditch and have it stay there. It’s not anchored. Forget that idea. 5. However, now that your side of the planet is covered in an anchored net of rope, do this: Tie off the bottom of the ladder to the anchored rope right at the top edge of the ditch, but so that it can pivot there. 6. Tie off two 21 meter lengths of rope to the ladder ‘top.’ Then push the ladder over (pivoting at it’s anchored bottom) the ditch and lowering it so that it stops short of horizontal. Tie off the 21 m. ropes. 7. Climb up onto the ladder, tie off some rope, and now, you can swing over (your body and initial jumb will have to make up for a missing half a meter or so. ```auto _ -_-_ \O/ | -_ - _ | | -_ - _ / \ --- | -------- | | | | | | | | | |------- | | | | | | | | | |------- | | | | | | | |------- | | | | | | | __________________ | ``` ## Peace. Or, once you’ve anchored your side of the planet with a knotted net, use the ladder as a pole vault. ---
**Author:** ![spinky](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@spinky](https://boards.straightdope.com/u/spinky)\ **Post date:** [May 18, 2003, 7:19pm UTC](https://boards.straightdope.com/t/logic-problem/175515/42 "2003-05-18T19:19:44Z")
> [@](#): > > \*Originally posted by The Great Unwashed \* > Surely the ditch has a rectangular cross-section, but even if it were triangular no angle would need to be specified as we know the base and height are both 40m Doh! Of course. I still agree that, as specified, it should be assumed it’s rectangular. > [@](#): > > I’m not sure that we can anchor ropes at any points on the far side of the ditch, not even at point “B” at the foot of the far side – running a taut line between A and B, what stops B moving towards the near side? Yeah, I thought of this too. The only reasonable answer is friction, which some people have assumed doesn’t exist, but I think that’s a ridiculous constraint (after all, if there were no friction, we wouldn’t even be able to walk towards the ditch to try to get to the other side). I did think of one **un** reasonable answer: the depth of the ditch could be constant _relative to the spherical surface of the planet_, which would mean the bottom was actually itself a section of a sphere, so a loop of unstretchable rope tied around one edge of the bottom of the ditch would not be able to slide. But we don’t have to resort to such silliness if we just allow friction. ---
**Author:** ![aahala](https://avatars.discourse-cdn.com/v4/letter/a/a88e4f/32.png) [@aahala](https://boards.straightdope.com/u/aahala)\ **Post date:** [May 18, 2003, 8:21pm UTC](https://boards.straightdope.com/t/logic-problem/175515/43 "2003-05-18T20:21:45Z")
Unless the planet is much smaller than the earth, the idea of running the rope around its circumference is much more timing consuming, and will take much more effort than the previous idea of just building a pile of rope in the trench. If the planet is about the size of the earth and the cross section of the rope is l/4" by l/4", then “one lap” of rope is roughly a cube 23 yards, which is enough along with the ladder to get across. ---
**Author:** ![Shade](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@Shade](https://boards.straightdope.com/u/Shade)\ **Post date:** [May 18, 2003, 8:28pm UTC](https://boards.straightdope.com/t/logic-problem/175515/44 "2003-05-18T20:28:49Z")
> [@](#): > > \*Originally posted by ntucker \* > **The only reasonable answer is friction, which some people have assumed doesn’t exist, but I think that’s a ridiculous constraint (after all, if there were no friction, we wouldn’t even be able to walk towards the ditch to try to get to the other side).** Swimming? Farting? ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [May 18, 2003, 8:41pm UTC](https://boards.straightdope.com/t/logic-problem/175515/45 "2003-05-18T20:41:33Z")
> [@](#): > > \*Originally posted by aahala \* > If the planet is about the size of the earth and the cross section of the rope is l/4" by l/4", then “one lap” of rope is roughly a cube 23 yards, which is enough along with the ladder to get across. First of all, I get that the cube is only 18.8 yd across. Second, what makes you think that the rope will stand in a cube formation? And third, even if it did, the chasm is 40 meters across; a 23-yard cube won’t reach. If you managed to make the rope into a dune 20 meters high, 40 meters along the edge, and with a slope angle of 30°, you’d need 27712 m[sup]3[/sup] of rope. This is enough to wrap around the Earth 22 times. ---
**Author:** ![spinky](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@spinky](https://boards.straightdope.com/u/spinky)\ **Post date:** [May 18, 2003, 10:13pm UTC](https://boards.straightdope.com/t/logic-problem/175515/46 "2003-05-18T22:13:10Z")
> [@](#): > > \*Originally posted by Shade \* > \*\*Swimming? Farting? \*\* 😛 I’ll weasel out of this one by claiming that without friction, life as we know it (and therefore swimming and farting) would not be possible. ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [May 19, 2003, 7:56am UTC](https://boards.straightdope.com/t/logic-problem/175515/47 "2003-05-19T07:56:02Z")
I suppose if you walked halfway around the planet along the ditch you could define that point as “the other side of the ditch” just along a different axis. The riddle might also be a trick question where you are supposed to answer how you get to the other side of the planet, allthough I find the verbal trickery is rather crude in this case if that is what it is. ---
**Author:** ![Beer\_Penguin](https://avatars.discourse-cdn.com/v4/letter/b/ad7895/32.png) [@Beer\_Penguin](https://boards.straightdope.com/u/Beer_Penguin)\ **Post date:** [May 19, 2003, 8:14am UTC](https://boards.straightdope.com/t/logic-problem/175515/48 "2003-05-19T08:14:41Z")
What the hell’s on the other side of the planet? ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [May 19, 2003, 9:17am UTC](https://boards.straightdope.com/t/logic-problem/175515/49 "2003-05-19T09:17:21Z")
Only the other side. ---
**Author:** ![mrcrow](https://avatars.discourse-cdn.com/v4/letter/m/838e76/32.png) [@mrcrow](https://boards.straightdope.com/u/mrcrow)\ **Post date:** [May 19, 2003, 9:37am UTC](https://boards.straightdope.com/t/logic-problem/175515/50 "2003-05-19T09:37:56Z")
if you can cut the ladder and anchor the ropes to each end after intertwining it through the rungs you could end up with a ladder/rope braid structure…it may not touch both sides and saga a bit… there is no mention of tools so that is just a musing. a rope ladder could be formed to descend and a rope coil to ascend…? will this ever reach you ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [May 19, 2003, 10:45am UTC](https://boards.straightdope.com/t/logic-problem/175515/51 "2003-05-19T10:45:26Z")
Is there a way to get the official answer to this problem after everyone is done mulling it over so we can see if we were right? ---
**Author:** ![Paradigm](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Paradigm](https://boards.straightdope.com/u/Paradigm)\ **Post date:** [May 19, 2003, 11:14am UTC](https://boards.straightdope.com/t/logic-problem/175515/52 "2003-05-19T11:14:35Z")
Since gravity is not mentioned in the question, I can to assume that the world has very low density and therefore a low gravitational attraction. So simply, A - jump the gap 😉 ---
**Author:** ![The\_Great\_Unwashed](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_great_unwashed/32/4791_2.png) [@The\_Great\_Unwashed](https://boards.straightdope.com/u/The_Great_Unwashed)\ **Post date:** [May 19, 2003, 12:29pm UTC](https://boards.straightdope.com/t/logic-problem/175515/53 "2003-05-19T12:29:10Z")
> [@](#): > > \*Originally posted by Paradigm \* > \*\*Since gravity is not mentioned in the question, I can to assume that the world has very low density and therefore a low gravitational attraction. > > So simply, > A - jump the gap 😉 \*\* [QUOTE] \*Originally posted days ago by Sock Munkey \* **If the planet is fairly small, say the size of one of the moons of mars, the gravity would be low enough to just jump across.** I’m afraid **Paradigm** that you owe **Sock Munkey** £5. Oh, and “Bingo!” ---
**Author:** ![The\_Great\_Unwashed](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_great_unwashed/32/4791_2.png) [@The\_Great\_Unwashed](https://boards.straightdope.com/u/The_Great_Unwashed)\ **Post date:** [May 19, 2003, 12:30pm UTC](https://boards.straightdope.com/t/logic-problem/175515/54 "2003-05-19T12:30:38Z")
::ahem:: > [@](#): > > \*Originally posted by Paradigm \* > \*\*Since gravity is not mentioned in the question, I can to assume that the world has very low density and therefore a low gravitational attraction. > > So simply, > A - jump the gap 😉 \*\* > [@](#): > > \*Originally posted days ago by Sock Munkey \* > **If the planet is fairly small, say the size of one of the moons of mars, the gravity would be low enough to just jump across.** I’m afraid **Paradigm** that you owe **Sock Munkey** £5. Oh, and “Bingo!” [Previous page](https://boards.straightdope.com/t/logic-problem/175515.md?page=2)