Calculating Magnetic Force with Vectors

[fight_club_alum]

Homework Statement

What is the magnitude of the magnetic force on a charged particle (Q = 5.0 μC) moving
with a speed of 80 km/s in the positive x direction at a point where Bx = 5.0 T, By = –4.0 T,
and Bz = 3.0 T?
a . 2.8 N
b. 1.6 N
c. 1.2 N
d. 2.0 N <- answer
e. 0.4 N

Relevant Equations

F = Q V X B

8000	0	0
5	-4	3

F = (5 x 10^-6) * up (sorry can't write a materix here)
F = (5 x10^-6) {0i - 24000 j - 32000 k)
F = -0.12 j - 0.16 k
Mag of F = 0.2 (I feel that there is something wrong in the question; I don't know)

 

[TSny]

80 km/s is not equal to 8000 m/s. Otherwise, your work looks good to me.

 

[gneill]

(sorry can't write a materix here)

Actually you can if you use LaTeX syntax:
$$
\begin{bmatrix}
1 & 2 & 3 & 4 \\
a & b & c & d \\
x & y & z & w
\end{bmatrix}
$$
See the LaTeX tutorial page: just follow the LaTeX Guide link you'll find underneath the reply box.

 

[gneill]

Here's an example of using LaTeX to show a vector cross product:
$$\begin{bmatrix}
v_i \\
v_j \\
v_k
\end{bmatrix} \times
\begin{bmatrix}
B_i \\
B_j \\
B_k
\end{bmatrix} =
\begin{bmatrix}
B_k \cdot v_j - B_j \cdot v_k \\
B_j \cdot v_k - B_k \cdot v_i \\
B_j \cdot v_i - B_i \cdot v_j
\end{bmatrix}
$$