Answer
a) $ 220 kJ$
b) $ -490 kJ$
Work Step by Step
We know that work is equal to change in kinetic energy. Recall, it is necessary to convert kilometers per hour into meters per second in order to do this problem. Thus:
$W = \frac{1}{2}m(v_f^2 - v_0^2)$
a) $W = \frac{1}{2}(1400)(26.4^2 - 19.4^2) = 220 kJ$
b) $W = \frac{1}{2}(1400)(0^2 - 26.4^2) = -490 kJ$
