Weight + speed = how many pounds

[kermit911]

I have a 165 lb dog that can run up to 15 mph with a 15 foot cabe as a leash. What I need to know is how stong does my leash have to be to hold her back? It's a Saint Bernard dog.
Second, that leash is going to be conected to a runner so the dog can run back and forth. The runner is about 60 feet long. How strong does the runner have to be? Example 1000 lb test... etc.

Thanx all

[shaun_04]

I take it you're a yank, hence the imperial.
How do you mean when you're talking about the strength of a runner? - how is it fixed? - do you mean breaking stress of the runner, or the force required to uproot it from the ground (if it is fixed into the ground).

[fo3nix]

your dog is about 75kg, and 15mph is about 6.7 metres per second.

momentum = mass * speed = 503 kgm/s

assuming force averaged over a second, that's about 500N of force.

[Loosehead]

Take no notice of the metric mafia, we use mostly imperial in UK too, much to their chagrin.

Sorry I have no idea how to work out the effective strain but I know what you mean!

[Space]

the big bad evil Metric Mafia is back ! War is upon us! Quick, Loosehead, to arms! fend them off!

The problem here is that we don't know how quickly the dog should be stopped. fo3nix assumed it is 1 second, I found it a bit optimistic at first, but actually it depends how strong your arm is. 500N is a lot of force, it is enough to make you fall if you are skinny...

So I actually think that for a such a big dog, it doesn't matter how fast or heavy the dog is, the rope just has to be strong enough to handle the force that you can handle yourself.
The heavier and stronger you are, the quicker the dog will be stopped.
So I think the answer is: get a rope that can handle your own weight. If it breaks, it means you would have fallen over with a stronger rope.