8-65 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m&=82\ut{kg}\\ v_i&=16\ut{m/s}\\ \Delta y &=4.2\ut{m}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$ \put \begin{cases} \KE : \text{Kinetic Energy}\\ \GE : \text{Gravitational Potential Energy}\\ \end{cases} $$ $$\Sigma \Delta E=0,$$ $$\Delta \KE+\Delta \GE=0$$ $$ \begin{aligned} \Delta \KE&=-\Delta \GE\\ \KE_f-\KE_i&=-\Delta \GE\\ \end{aligned} $$ $$ \begin{aligned} \KE_f&=\KE_i-\Delta \GE\\ &=\frac{1}{2}m{v_i}^2-\Delta (mgy)\\ &=\frac{82}{5} (640-21 g)\\ &=7118.58974\ut{J}\\ &\approx 7.1\times10^3\ut{J}\\ &\approx 7.1\ut{kJ}\\ \end{aligned} $$