Some little questions, please answer

Considering that the direction of velocity is positive if directed towards the sky and it is negative if directed towards the ground:
v = v0 - g*t
v0 is the velocity at the beginning, g the gravitational acceleration, t the time passed from when the velocity was v0, v the velocity at the time t.
At its highest point in space, the rocket must have velocity v=0 because it is inverting its direction in that moment, which means that it went from a positive velocity (towards the sky) to a negative velocity (towards the ground).

Therefore the initial velocity is the solution for v0 of:
0 = v0 - g*t --> v0 = g*t
(that you can calculate since you know the time when it reached the highest point and the gravitational acceleration)

Now we can calculate the height, reminding the formula for the uniform acceleration (deceleration):
spacetraveled = timepassed* (initialvelocity+finalvelocity)/2
and substituting the data of this case:
height = t * (v0 + 0)/2
(you just calculated v0 and you already knew t, so now you can find the height)

The energy at the beginning is only kinetic energy, which can be calculated with the formula:
Ek=(m * v0^2)/2
You already calculated v0 but you don't know the mass of the rocket. Every other object could have done exactly the same thing (going up in same time with same velocity and same height), so the only thing that can help is to know its mass. Was the mass (g or lbs) of the bottle written somewhere on it?
If it were full of water, the fact that it is a 2L bottle and knowing that density of water is more or less 1kg/L, then you would know that the mass of the bottle (ignoring the container) was mass = density*volume=1kg/L * 2L = 2 kg. Then you could find the energy.
But if it was empty to know that it was a 2L bottle doesn't help, because you need the mass, not the volume.

A Watt, the unit of measure for Power, is a Joule per second: 1W=1J/s,
which means that it is (at least in this case): Power= Energy/time
Therefore, if you know the Power P(=60W) and the Energy E(which you should have found before, knowing the mass of the bottle), you can find the time:
t = P/E

Whatever we hear is always a wave (or waves) which propagate mainly through the air (but in general propagate in all materials in different ways).
But did it have water inside or not?