Calculating velocity or acceleration

[newton2008]

for our physics project we had to build a catapult
and our group built a kind of ballista.. if u don't know what that is it's a type of catapult that shoots out the object instead of launching it like a see-saw
so our catapult is hooked up to a spring which you pull back.. then release it to launch a marble through a pipe
but we need to find the velocity of our marble when it's launched
how am i supposed to do that?

i'm thinking i could use the spring constant somehow.. but i don't have any ideas on how to apply it

any help appreciated guys :)

 

[pchalla90]

Potential energy from a spring is calculated by the formula U=(1/2)kx^2, where k is the spring constant, and x is the change in the length of the spring.

Plug in the values for k and x and you have a value in Joules. Then set that as equal to E(k)=(1/2)mv^2, where m is mass, and v is velocity.

Voila, you have the initial velocity!