Hello!
We can use the following equation for magnetic force on a charged particle:

= Magnetic force (N)
q = Charge of particle (1.6 × 10⁻¹⁹ C)
v = velocity of particle (5.2 × 10⁷ m/s)
B = Magnetic field strength (1.4 T)
This is a cross-product, so the equation can be rewritten to F = qvBsinφ where φ is the angle between the magnetic field and particle velocity vectors.
Since the proton's velocity vector and the magnetic field vector are perpendicular, sin(90) = 1. We can reduce the equation to:

Plug in the known values.
