An electron, charge e, mass m, enters a uniform magnetic field 
 ˆ B Bi with an initial velocity
  
x y
v v ˆi v ˆj . What is the velocity of the electron after a time interval of t second?

Dear Student
x component of velocity remains unchanged as it parallel to the magnetic field.
velocity along j as there is no force along j direction
but velocity along k direction is given by a*t = qvB/m *t
Hope it helped