## Essential University Physics: Volume 1 (3rd Edition)

a) $220 kJ$ b) $-490 kJ$
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) $W = \frac{1}{2}(1400)(0^2 - 26.4^2) = -490 kJ$