4) Protons moving horizontally at a speed of 100 km/s enter into a region with uniform electric field that extends a distance d = 3.00 cm, as shown below. The electric field is directed vertically, as shown. We wish for the protons to be deflected through a 15.0 angle when they emerge on the right side. That means that the final velocity vector makes a 15 angle with the initial velocity vector. What is the necessary magnitude of the electric field to accomplish this? Hint: How is this problem similar to a horizontally launched projectile? d E answer: 932 N/C