Calculating electric field given velocity and magnetic field

[RKOwens4]

Homework Statement

In the figure below, an electron moves at speed v = 93 m/s along an x-axis through uniform electric and magnetic fields. The magnetic field B is directed into the page and has magnitude 4.00 T. In unit vector notation, what is the electric field?

Figure: http://imageshack.us/photo/my-images/233/webassign2.jpg/

Homework Equations

v=E/B

The Attempt at a Solution

I know that the answer is 0 for the i and k direction. I thought for the j direction, I just had to use the formula v=E/B, which would give me 372. But that's incorrect. I don't know what else to try.

 

[rock.freak667]

Have you tried -372 ?

 

[RKOwens4]

That did it! Thanks.

 

[rock.freak667]

That did it! Thanks.

Good. Usually when they don't specify a direction for the z-axis, you will need to try both + and - signs.

 

[vela]

Note that getting the sign right isn't a matter of guessing. From the right-hand rule, you should be able to see that the magnetic force will point in the +y direction. To cancel it, the electric force must point in the -y direction.