Problem: A proton moving at 6.5x10^6 m/s encounters an electric field of 4500 volt/meter. How fall will the proton penetrate the field before stopping. (Electric field and proton are moving in opposite directions) My attempt: First I found the kinetic energy of the proton, then I found the force that the electric field exerted on the proton with F=Eq. The force would do the sane amount of work on the proton as the kinetic energy the proton had to make it stop so I used w=fs with w=kinetic energy and solved for s. The answer was 49m but the answer in the book is 10.49m. Can someone tell me where I went wrong?