A charged particle enters a uniform magnetic field perpendicularly and experiences a force F. if the kintetic energy of the particle is doubled, then what will be the force on that particles ?

Explanation

Force on a charged particle entering a mangetic field B perpendicular with speed v is, `F=qvB`
or, `F prop v`
Now, kintetic energy, `E prop v^(2)`.
or, `F prop sqrt(E)["since" F prop v]`
or `(F)/(F)= sqrt((E)/(E))`
or, `F'=Fsqrt((E)/(E))=F sqrt(2)`.