Answer
It takes $~~810~seconds~~$ for the electrons to get from a car battery to the starting motor.
Work Step by Step
We can find the electron drift speed:
$J = n~e~v_d$
$v_d = \frac{J}{n~e}$
$v_d = \frac{i}{A~n~e}$
$v_d = \frac{300~A}{(0.21\times 10^{-4}~m^2)(8.49\times 10^{28}~m^{-3})(1.6\times 10^{-19}~C)}$
$v_d = 1.05\times 10^{-3}~m/s$
We can find the time:
$t = \frac{distance}{speed}$
$t = \frac{0.85~m}{1.05\times 10^{-3}~m/s}$
$t = 810~s$
It takes $~~810~seconds~~$ for the electrons to get from a car battery to the starting motor.
