Problem is http://imgur.com/bQIFJ
I presume F=BIl and E=Blu.
The Attempt at a Solution
Not very well. I don't really understand how to start the question so if I could get some nudges in the right direction that'd be great. I'm not sure how the speed of the van comes into play here. I gather that I'll have to work out V once for the 38uT field density and then again for the 42uT and get the difference.