AQA-PHYA4-1-QP-JUN14 Question 23

Hello,

How did the mark scheme arrive to this solution?

23) Two electrons, X and Y, travel at right angles to a uniform magnetic field. X experiences a magnetic force, Fx, and Y experiences a magnetic force, Fy.

What is the ratio Fx/Fy if the kinetic energy of X is half that of Y?

Answer: D 1

Thank you!

First you find v for both by rearranging the KE equation
so v= square root (2Ek/m)
This is the v for X
Then v for Y, would have 2Ek instead of Ek:
v=square root(4Ek/m)
And so Bqv(x)/Bqv(y) where B and q cancels come to 1/square root 2
The answer is C btw not D
Hope it helps

Thanks for the answer I get it now!
But that's weird the answer really says D.

It's June 2015 Q23 not June 2014 maybe that's why