Scorched Tanks/Earth: Magnetic Shield Help (please)

I never took Physics so this is nearly impossible (I got as far as Trig)
for me. How do I make a projectile fired from a tank behave the same way
it does in Scorched tanks when it comes in contact with the "Magnetic
Field" of a magnetic shield.

I am sure it has something to do with once the projectile enters the field
for the first time I take the current information of the projectile in
flight and apply this into a new formula that uses the force of the of the
magnetic field as part of the new vector(s)... (???)

Again, I have not taken Physics so my terminolgy is off somewhat (alot?).

I can't seem to figure out how to do this. Finally, when it leaves the
field, we would disregard that new formula and create another one to affect
the projectile flight. But how.

I know I am asking alot, and I have tried reading up on physics in my wifes
college books and on the net to no avail. I am stumped. Please help with
some code, if you would. In BASIC code ;^)

Oh, *one last thing* I read something on this group about Euler method
(which I guess I am using) and some other method (the name escapes me).
Which sould I use for a 2D clone of Scorched Tanks/Earth ?