Question

if a proton is moving at a speed of 5 m/s to the right through a uniform magnetic field that points to the left, which of the following describes the force the proton feels?

Answer 1

Here you did not supply the figure and other data. I am giving you the idea how you can determine the magnetic force.

F = qvB sin Direction of magnetic field Moving charge v sin

Here, v = 5 m/s and it is moving right to the direction of magnetic field, hence $\inline \theta =90^{o}$ . Therefore, the magnetic force experienced by the proton will be F = qvB, where q is the charge of proton. If you know the values of q, v and B, you can determine the force.