Particle energy through magnetic and electric field

[Sonko]

Homework Statement

Given the formula for the force on a charge in an electric and magnetic field is F = eE + ev X B
why can the magnetic fi eld never increase the energy of a particle that travels through
it

Homework Equations

N/A

The Attempt at a Solution

I really am not sure! I look at this and i know that the reason must be obvious and I'll kick myself for not getting it but I'm simply at a loss! The only thing i can think of right now is that the fields are perpendicular to the motion and will cancel out however this just doesn't make sense!
Any help would be appreciated in not just helping me find the answer but for helping me rid myself of the stupidity I'm feeling! Thanks

 

[kuruman]

When does the kinetic energy of particle increase? In other words, how does energy get pumped into the particle?

 

[Sonko]

umm I'm not completely sure what you mean? do you mean to use E^2 = p^2 + m^2 and show there is no overall change in momentum?

 

[kuruman]

This is not necessarily a relativistic situation. If the kinetic energy of a particle increases, this means that there has been an energy transformation. What must be done on the particle to achieve this energy transformation? Hint: It starts with "W".

 

[Sonko]

i woke this morning and came to my sense using your first clue! showing that Work done (and so the change in energy) was not increased.

thanks for the help on the subject!