a particle is acted upon by a force of constent magnitude which is always perpendicular to the velocity of the particle. motion of the particle takes place in a plane. then what is constant ?

magnitude of velocity, kinetic energy,etc.

the motion is circular motion and magnitude of force is mv^2/r where r is the radius of the circular path.

it will do circula motion with constant speed and kinetic energy.

it will do circular motion as it satisfies the condition of circular motion

next the constant things are total energy and centripetal force