That is, force is acting along Z-axis.
(i) For a beam of charged particles to pass undeflected crossed electric and magnetic fields, the condition is that electric and magnetic forces on the beam must be equal and opposite i.e.,
(ii) The beam strikes the target with a constant velocity, so force exerted on the target is zero.
However, if proton beam comes to rest, it exerts a force on the target, equal to rate of change of linear momentum of the beam i.e
where n is the number of protons striking the target per second.