JEE Main · 2006 · 30 Apr 2006 · Offline · Magnetic Effects of Current

The particle starts from rest, so its initial velocity is zero and the magnetic force $q\vec{v}\times \vec{B}$ vanishes. The electric force $q\vec{E}$ then sets it moving along $\vec{E}$, which is parallel to $\vec{B}$. The velocity it acquires therefore stays parallel to $\vec{B}$, so $\vec{v}\times \vec{B}$ remains zero at every instant and no magnetic force ever acts. The particle simply accelerates along the common direction of the fields, tracing a straight line.