A uniform magnetic field of 0.25 T points vertically downward. A proton enters the field with a horizontal velocity of 4.0 * 10⁶ m/s north. What are the magnitude and direction of the instantaneous force exerted on the proton as it enters the magnetic field?
1) 1.6 * 10⁻¹³ N west
2) 1.6 * 10⁻¹³ N downward
3) 1.6 * 10⁻¹³ N east
4) 1.6 * 10⁻¹³ N upward