(a) $v = \frac{dx}{dt} = 3 - 8t + 3t^{2}$ $\therefore v_{0} = 3\ m/s$ and $v_{4} = 19\ m/s$ $W = \frac{1}{2}m(v_{4}^{2} - v_{0}^{2})$ [According to work energy theorem] $= \frac{1}{2} \times 0.03 \times \left( 19^{2} - 3^{2} \right) = 5.28\ J$
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Ph.D. in Physics with 19+ years of teaching experience.