1. The problem statement, all variables and given/known data A proton (mass= 1.67×10-27 kg, charge= 1.6×10-19 C) traveling with speed 1×106 m/s enters a region of space containing a uniform magnetic field of 1.2 T. The magnetic field is coming out of the screen. What is the time t required for the proton to re-emerge into the field-free region? 2. Relevant equations qvB = mv2/R 3. The attempt at a solution I begin by solving for R using the above equation: R= (mv)/(qB) Since the proton moves in and then back out it completes a semi-circle. The distance traveled is then πR as it is half of the circumference of a circle. The velocity does not change for the entire distance traveled so dividing distance by velocity should give me the time. This comes out as incorrect though. I am unsure as to what I am doing wrong.