Write the condition under which an electron will move undeflected in the presence of crossed electric and magnetic fields?

A particle of charge q is moving with velocity v in the presence of crossed electric field E and magnetic field B as shown. Write the condition under which the particle will continue moving along x-axis. How would the trajectory of the particle be affected if the electric field is switched off?

An electron beam with equivalent electric current I enters a region of crossed electric field and magnetic field B. Both the fields are uniform. It is found that the electron beam goes undeviated through the region of fields. After passing the field region, electrons hit a grounded target. How much force is exerted by the electron beam on urget? Assumem is the mass of electron and e its charge.