The magnetic force acting on a chared particle moving in a magnetic field is always perpendicular to the velocityof the particle. So the charged particle moves in a circle whose plane is perpendicular to the magnetic field.
For the electric field; a charged particle between the plates: x = v
o t , solve for t and plug into y = 1/2 a t
2. We see that y is proportional to x
2. Henc, the trjectory is a parabola.
y = 1/2 a ( x/vo )2 = 1/2 a (x2 / vo 2 )