Along, straight, horizontal wire carries current toward the east. a proton moves toward the east alongside and just south of the wire. what is the direction of the magnetic force on the proton?

north direction.

Explanation:

The wire carries a current towards the east . The magnetic field will make circular path around the wire in clockwise direction  so at a point just south of wire , magnetic field will be into the plane of paper containing wire. If we take east as x -axes , north as y axes then out of plane will form z axes. Hence direction of magnetic field will be -  z direction .

Magnetic field can be represented as - B k

Proton is moving towards east ie in + x direction so it can be represented as follows

velocity = V i

Force F = q( V i x -B k)

= ( BqV) j or + ve j direction or along north direction

So direction of force will be along north direction.

real, smaller and upside-down.   so the answer should be b.

no. dot product   =0 when vecs at right angles