1. The problem statement, all variables and given/known data A proton is moving through a vertical magnetic field. The (instantaneous) velocity of the proton is 8.5x105m/s horizontally in the north direction. The (instantaneous) acceleration produced by the magnetic force is 2.90x105m/s2 in the west direction. What is the magnitude of the magnetic field? 2. Relevant equations Proton Mass = 1.67x10-23 kg Proton Charge = +e = 1.60x10-19 C B = F/(qv) (I think!) 3. The attempt at a solution Okay, this seems like it should be simple, but the online homework keeps saying I am wrong, so obviously I am skipping something here. First, applying Newton's second law, I found the force, F, required of the Magnetic Force to produce the acceleration (F=ma = (1.67x10-23 kg x 2.90x105 m/s2 = 4.843x10-18 N). Then, all I need to do is put this force in the equation for a charged particle in motion in a magnetic field, which I think is B=F/(qv), so I should get, B = (4.843x10-18 N)/[(1.60x10-19 C)(8.5x105m/s), which gives me B = 3.561x10-5 Tesla. But apparently that is wrong. Am I missing something small, like a number, or do I have the wrong equation? Thanks!