8-39 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} v_i&=610\ut{m/s}\\ m&=40\ut{g}=0.04\ut{kg}\\ d&=12\ut{cm}=0.12\ut{m}\\ v_f&=0 \end{cases} $$ $$ \put \begin{cases} \KE : \text{Kinetic Energy}\\ \TE : \text{Thermal Energy}\\ \ME : \text{Mechanical Energy}\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \Delta \ME&=\Delta \KE\\ &=\Delta \(\frac{1}{2}mv^2\)\\ &=\frac{1}{2}m\Delta \(v^2\)\\ &=\frac{1}{2}m \({0}^2-{v_i}^2\)\\ &=-\frac{1}{2}m{v_i}^2\\ &=-7442\ut{J}\\ &\approx -7.4\ut{kJ}\\ \end{aligned} $$ $$\ab{b}$$ $$\Sigma \Delta E=0,$$ $$\Delta \TE+\Delta \ME=0$$ $$ \begin{aligned} \Delta \TE&=-\Delta \ME\\ fd&=-\Delta \ME\\ \end{aligned} $$ $$ \begin{aligned} f&=\frac{-\Delta \ME}{d}\\ &=\frac{186050}{3}\\ &\approx 62016.666666666664\ut{N}\\ &\approx 6.2\times10^4\ut{N}\\ &\approx 62\ut{kN}\\ \end{aligned} $$