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Relating to a previous question, say that a group of people is hunting an elephant-sized land animal. For some reason, this animal needs to be harpooned so it won't simply run away to an inhospitable terrain where the hunters couldn't reach it in a timely manner. Assuming there is only one harpoon and it's securely attached, what is the minimum rope strength needed hold back the animal?

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    $\begingroup$ If your your using your harpoons in the traditional way they use them to hunt whales (you stick your harpoons in then let the whale drag your boat around until it's too exhausted to run any more) your rope only needs to be strong enough to carry the weight of the hunters laden craft 🤔 [imagines wheeled carts bouncing along behind a bellowing elephant] 🤪 $\endgroup$
    – Pelinore
    Sep 8, 2022 at 8:55
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    $\begingroup$ keep in mind keeping the harpoon in the elephant is going to me much harder than the rope, if fairly narrow rope will be a lot stronger than that hold. whalers often hit whales with multiple harpoons for a reason. $\endgroup$
    – John
    Sep 8, 2022 at 20:33

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An adult elephant can run at a top speed of 25 MPH, and weigh over 10 tons. That's a lot of energy that would to be dissipated almost instantly to bring a charging elephant to a full stop without snapping the rope.

A rope would need to handle over a meganewton of force to decelerate 10,000kg from 11m/s to a standstill in a tenth of a second. To put that in perspective a quality static rope used in safety applications will have a rated breaking strength around 30kN. It would be prudent to factor in a safety margin on top of the MN minimum, unless you want your rope breaking unexpectedly.

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  • $\begingroup$ So if the deceleration is over 5 or 10 seconds, that makes it feasible, right? 30 kN becomes sufficient. $\endgroup$
    – user86462
    Sep 8, 2022 at 11:17
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    $\begingroup$ @Sean If the deceleration is over 5 seconds, then an elephant starting at 11ms-1 will have moved 27.5m during that time. So now you need elastic cord, not standard rope, and I suspect that breaking strength on elastic is going to be lower than the rope. Also, there's no point in making the deceleration time longer than the elephant's acceleration time, otherwise it's strong enough to break the tether by pulling on it. (Unless you go with the 'harpoon it from a cart' system rather than anchoring to a tree...) $\endgroup$
    – Toby Y.
    Sep 8, 2022 at 12:37
  • $\begingroup$ @SeanOConnor The 30kN figure is for static rope which has no stretch. Dynamic ropes which do stretch apply less than 10kN and aren't load rated. They're just rated to catch an 80kg weight falling 4m 5 times without breaking. $\endgroup$
    – sphennings
    Sep 8, 2022 at 13:06
  • $\begingroup$ @MArifRahmanWinandar A rope with just the right length gets you a guaranteed miss if you underestimate the distance. A stationary elephant when harpooned will have twice the length of the rope to accelerate. This may be less than what is needed to reach top speed. All this is assuming a stationary elephant. Using top speed gives us an upper bound on the minimum rope strength needed for all situations, (you may also want to factor in a safety margin). $\endgroup$
    – sphennings
    Sep 8, 2022 at 15:31
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    $\begingroup$ @MArifRahmanWinandar That's not indicated anywhere in the question. We answer questions as they are written. I've given you a serviceable upper bound. Generally speaking when dealing with any large animal you want to have solid safety margins in place. A husbandry guide I found recommends buildings built to withstand the force of a full grown elephant moving at max speed, with similar numbers to what I used above. $\endgroup$
    – sphennings
    Sep 8, 2022 at 16:01

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