Finding the magnetic force on a moving charge?

Question

Q:

An electron moves in the magnetic field B= 0.550i^ T with a speed of 0.700 X 10^7 m/s in the directions shown in the figure( http://session.masteringphysics.com/prob... ). For each, what is magnetic force F on the electron? Give your answers in component form (ie Fx, Fy, Fz)

I understand how to do part A, but part B is still stumping me. Can anyone explain this to me?

Answer 1

referred website is not showing figure

i can not know which direction the velocity vector>

F = q [v cross B]

let (v) be in y-z plane

v = [vy (j) + vz (k)]

where |v|^2 = vy^2 + vz^2 = (0.7*10^7)^2

|B| = 0.550 T

Fx (i) + Fy(j) +Fz(k) = (-e)| |B| [(vy j + vz k) cross (i)]

use vector product on rightside

Fx (i) + Fy(j) +Fz(k) = (-e) |B| [vy (j cross i) + vz (k cross i)]

Fx (i) + Fy(j) +Fz(k) = (-e) |B| [vy ( -k) + vz (j)]

Fx (i) + Fy(j) +Fz(k) = [e  |B| vy] (k) + [- e |B| vz] (j)

comparing the coefficientsof (i, j, k) on both sides

Fx =0

Fy= [- e |B| vz]

Fz = [e  |B| vy] ----------- (1)

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it is possible that your vy=0 or vz =0

put in (1) accoringly

if v is inclined at an angle in y-z plane

tan (angle) = vz/vy = known

vy^2+vz^2 = known

you can find F's

hope i could gather it correctly