Task with spring, energy, velocity and angle

1. The problem statement, all variables and given/known data
A projectile is loaded into a spring cannon.

Find its velocity as it leaves the spring.

The cannon is angled at 38 degrees above the horizontal. (?=38)

m=0.025kg
k=100 N/m
x0=0.13m
x1=0.05m

(We press the spring down 13 cm when we load it. When it stops expanding, it still has 5 cm of winding left. Bit ambiguous in the text, but I interpret this to mean there is some mechanism that stops it from expanding the full 13 cm)

2. Relevant equations

0.5*k*x^2
0.5*m*v^2
mgh

E(initial) = E(final)

3. The attempt at a solution

Do I have to account for the angle to find the velocity as it leaves the spring?

Please correct me on this:

1) The energy contribution from the spring does not need to be vectorized, because it is angled in parallell with the angle of the velocity we're measuring.

2) The contribution from gravity also does not need to be vectorized, because when there is no friction, all the gravity will push against the spring direction regardless of angle. This one I am really unsure of..

If I pretend the cannon points completely vertically:

3) If statement 3 is correct: all angles for the cannon between 90 and 0 will give the same velocity.
If statement 3 is incorrect, and the retarding contribution from gravity changes with angle, surely 90 degrees (completely vertical) will give the lowest velocity, and 0 degrees with give the highest.

This conflicts with my calculations of 7.69 m/s for vertical, because the answer given is only 7.53 m/s

What am I doing wrong? Any help whatsoever would be appreciated, spent.. 4 hours on this simply task now hah!

Source: http://www.physicsforums.com/showthread.php?t=672477&goto=newpost

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