Proving that one quantity *eventually* surpasses the other I want to prove the following; $$\forall t>0\ \ \forall m\in \mathbb{N} \ \ \exists N \in \mathbb{N} \ \ \forall n\geq N: \ (1+t)^n > n^m.$$
For readers who hate quantifiers, here's the version in words: "$(1+t)^n$ eventually surpasses $n^m$ for some $t>0$ and $m\in \mathbb{N}$".
Though this sounds simple enough, I couldn't manage to prove it using only very elementary statements about the real numbers, like the archimedian property etc. (so no derivates and so on involved).
My questions are: 
1) Is there a simple (as described above) proof for this ? (If there isn't, I would also be happy with a proof using more of the analysis machinery.)
2) Is there a way to express the least $N$, which satisfies the above, in a closed form ?
3) I have somewhere heard of a theorem, that two real convex functions can have at most two intersection points (and the above statement seems closely related to this theorem), so I would be very happy, if someone could also give me a reference for this theorem.

For your question 1:
(1) Show $2^n > n$ for all $n$ immediately by induction.
(2) Moreover, given $c$ clearly $2^n> c$ for almost all $n$.
Lemma:
For $c>0$ and $m\in \mathbb N$, we have $2^n > c n^m$ for almost all $n$.
Proof by induction on $m$.
The case $m=0$ is just (2).
Assume the statement is true for some $m$.
We want to show that $2^n> c n^{m+1}$ for almost all $n$.
By induction assumption, there is $N$ such that $k>N$ implies $2^k>2^{m+2} c k^m$.
If $n>2N$ is even, write $n=2k$ with $k>N$. Then $2^n = 2^k\cdot 2^k>2^{m+2}c k^m\cdot k = 2c\cdot (2k)^{m+1} > c n^{m+1}$ (we use (1) in this).
If $n>2N$ is odd, write $n=2k-1$ with $k>N$. Then $2^n = \frac12\cdot2^{2k}>c\cdot (2k)^{m+1}>c n^{m+1}$. \qed
Finally, to change the base from 2 to $1+t$, select $r\ge\frac 1t$.
Then $(1+t)^r \ge 1+r t \ge 2$.
Hence if $n=k r - s$ with $0\le s < r$, then $(1+t)^n>\frac12 2^k> \frac12\cdot(2r^m) k^m=(rk)^m\ge n^m$ for almost all $n$.
--
For your question 3:
$x\mapsto x^4$ and $x\mapsto x^2$ are convex, but $x^4-x^2=0$ has three solutions $-1, 0$,and $1$. 
