When a charged particle enters a uniform magnetic field,its kinetic energy

Three ions $H^+$,$He^+$,and $O^{2+}$ having the same kinetic energy pass through a region in which there is a uniform magnetic field perpendicular to their velocity. Then:

An electron $(q = 1.6 \times 10^{-19}\, C)$ is moving at a right angle to a uniform magnetic field of $3.534 \times 10^{-5}\, T$. The time taken by the electron to complete one circular orbit is ...... $\mu s$.

Give an example of a situation in which an applied force does not result in a change in kinetic energy.

$A$ charged particle is moving in a uniform magnetic field in a circular path of radius $R$. When the energy of the particle becomes $3$ times the original, the new radius will be

$A$ monoenergetic beam of electrons moving along the $+y$ direction enters a region of uniform electric and magnetic fields. If the beam goes straight undeflected,then fields $B$ and $E$ are directed respectively along: