Answer
We can express the velocity in unit-vector notation:
$v = (1.5\times 10^5~m/s)~\hat{i}-(2.8\times 10^6~m/s)~\hat{j}$
Work Step by Step
In part (a), we found that the electron's acceleration in unit-vector notation is:
$a = (-2.1\times 10^{13}~m/s^2)~\hat{j}$
We can find the time it takes the electron's x coordinate to change by 2.0 cm:
$t = \frac{2.0\times 10^{-2}~m}{1.5\times 10^5~m/s} = 1.33\times 10^{-7}~s$
We can find the y component of the electron's velocity after this time:
$v_y = v_{0y}+at$
$v_y = (3.0\times 10^3~m/s)+(-2.1\times 10^{13}~m/s^2)(1.33\times 10^{-7}~s)$
$v_y = (3.0\times 10^3~m/s)-(2.8\times 10^6~m/s)$
$v_y = -2.8\times 10^6~m/s$
We can express the velocity in unit-vector notation:
$v = (1.5\times 10^5~m/s)~\hat{i}-(2.8\times 10^6~m/s)~\hat{j}$
