Is it possible to repay the world debt? If not, why do we care?
So there are a couple of things you want to consider:

1st: It is not true that if some country gains 1% some other country must have lost that 1% of economic growth. The economy is not a zero-sum game where the gains of one person are the losses of another one. In fact, usually, it is the opposite. Think about it this way, if the US grows by a lot it also means that they will buy more things from other countries so these countries will probably also grow faster. 

2nd: Money is just the means by which we keep track of, and do transactions. At the end, what really matters is how much stuff is produced (goods or services). That is why if some country produces more things, everyone can benefit from it. 

I do understand your logic that if the Bank produces 100B of coins how can they expect to get back 101B? Once you think of it in terms of stuff, the puzzle is resolved as follows:


The bank lends you the money so you can buy and plant seeds (these are the 10B), they expect to get back some of the benefits from this productive project after you produce apples (they could directly ask to pay back in apples, but this would be impractical, that's one of the reasons we use money, so instead  they ask you for the 10.1B). Of course, if the bank does not print more money where will the .1B come from? Well, indeed the bank will never ask for 1% interest if they know there is no physical way to actually pay it back. 
What really happens is that the bank understands that if an economy is growing, she needs to constantly be printing money, so people can easily do and keep track of all the transactions they do. Therefore, when they ask for the 1% interest, first this is possible, because there is more money out there in the economy, and second, they choose how much interest to charge in order to reflect that they expect you to do something productive with the money (interest also depend, of course, on how risky is your project, and other factors).


I am over-looking the whole issue of inflation to keep things simple and explain the main logic of why banks (including the central bank) charges interests. Whenever you think about whether a debt can be paid or not; the relevant question is not if there is enough money out there to pay it. Rather the relevant question is if the money loaned is being used in a productive way so that it can later pay the interests. And if the answer is no, we care because that means that the money loaned is being wasted, instead.