Answer
The magnetic force is $5.1 \times 10^{-13}~N$ and this force is directed to the north.
Work Step by Step
We can find the speed of the electron:
$\frac{1}{2}mv^2 = K$
$v^2 = \frac{2K}{m}$
$v = \sqrt{\frac{2K}{m}}$
$v = \sqrt{\frac{(2)(7.2\times 10^{-18}~J)}{9.1\times 10^{-31}~kg}}$
$v = 3.98\times 10^6~m/s$
We can find the magnetic force:
$F = q~v\times B$
$F = (-1.6\times 10^{-19}~C)(3.98\times 10^6~m/s)(0.800~T)$
$F = -5.1 \times 10^{-13}~N$
By the right hand rule, $v \times B$ would be directed south if the charge was positive. However, the negative charge results in a force directed to the north.
The magnetic force is $5.1 \times 10^{-13}~N$ and this force is directed to the north.
