Two proton beams are moving with equal speed, $v$ in the same direction. The ratio of electric force and magnetic force between them is -(Where $c_0$ is the speed of light in vacuum)

A particle of mass, $M$ and carrying charge, $Q$ is launched with initial speed, $v$ and at an angle of $\theta$ relative to the horizontal direction. When it reaches the maximum height it enters a region of the uniform magnetic field. In the region, it moves at constant velocity in the horizontal direction. Determine the direction and strength of the magnetic field.

Particle of charge $-e$ is moving with an initial velocity $\overrightarrow{v}$ when it enters midway between two plates where there gravitational force. The magnitude of the velocity of the particle if it just strikes the end of the plate?

The charges $1,2,3$ are moves in uniform transverse magnetic field then:-