posted by Sandhya .
A 160 MeV proton, moving in the x-direction, enters a region in which there is a magnetic field. The proton experiences an acceleration of 5.5 X 10^12 m/s^2 in the y-direction. What can you say about the magnetic field?
You should be able to say someting about B's component in the z direction.
Solve for V using E = (1/2) M V^2
Then use the vector equation F = q V x B