A charged particle enters into a gravity free space occupied by an electric field E and magnetic field B and it comes out without any change in velocity. Then, the possible cases may be

(1)  v  is parallel on anti-parallel to B.

(2) If E $\not\equiv$0, the charged particle will be accelerated and velocity will change .

(3)  qE + q(v $\times$ B) = 0

or     E = - (v $\times$ B) = (B $\times$ v )

(4) If B=0 ,E=0 and the space is gravity free , then velocity remains unchanged .