# In a certain region of uniform electric field E= -E0K^ and magnetic field B=B0K^ are present. At time t=0, a particle of mass m and charge q is given a velocity v=v0j^ + v0k^. Find the minimum speed of the particle and the time when it happens so.

$\\work done by magnetic field is zero \\F=-qE\vec k \\v will be minimum when k component of velocity becomes \\zero and then it will go negative but over all \\ magnitude will increase again \\so \\v_{min}=v \\=>a=qE/m \\=>t={vm \over qE}$