A railgun is a classic example of using the magnetic force to launch an object. Suppose the following railgun has up to 1m of rail length, and it is trying to launch a 4.5 kg projectile using a 2 T B-field. Assume that the only resistance is given to be 15 Ohms and the width of the projectile is 10 cm. What voltage and orientation (which side is + and which side is -) battery must we use if we want to launch the projectile at a speed of 90 m/s?