Question

If a proton enters perpendicularly a magnetic field with velocity

Answer 1

If there is no other force (like electric force, gravitational force etc.) acting on the electron, then its velocity remains unchanged.

Magnetic force acts on a charged particle only when its velocity has a non-zero component in the direction perpendicular to the magnetic field

Answer 2

When the proton enters perpendicularly in the magnetic field with velocity v, then the time period is T.

Now,

As it has entered perpendicularly therefore its time period will remain unchanged even if its velocity is increased to 2v.