Each bullet needs its own velocity. Why in the world you made that static I do not know.
Also, DO NOT LOAD A NEW IMAGE FOR EACH BULLET. Sorry the caps was rude. You can load an image once and then set the reference to other objects.
Image a b c;
a = load blah blah blah;
b = load blah blah blah;
c = load blah blah blah;
public class Bullet
public Bullet(your args)
image = a b c or what ever.
Sorry for bad formatting. I usually have a static class that has a reference to all images and then grab the reference when an object needs the image.
Image a = ImageResources.get("imagename");
This way you do not have a thousands of images loaded but only one.