Question

What is When v, E and B, all the three are Collinear?

Answer

When v, E and B, all the three are Collinear - In this situation, as the particle is moving parallel or anti-parallel to the field, the magnetic force on it will be zero and only electric force will act and so a = F/m = qE/m The particle will pass through the field following a straight line path (parallel field) with change in its speed.