8-11 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m&=50.0\ut{kg}\\ h&=8.00\ut{m}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$ \put \begin{cases} \KE : \text{Kinetic Energy}\\ \GE : \text{Gravitational Potential Energy}\\ \TE : \text{Thermal Energy}\\ \end{cases} $$ $$\Sigma E_i=\Sigma E_f,$$ $$ \begin{aligned} \GE_i&=\KE_j+\TE_j\\ \KE_j&=\GE_i-\TE_j\\ &=mgh-fh\\ &=400g-8f \end{aligned} $$ $$\ab{a}$$ $$f=0,$$ $$ \begin{aligned} \KE_a&=400g\\ &=3922.66\ut{J}\\ &\approx 3.92\times10^3\ut{J}\\ &\approx 3.92\ut{kJ}\\ \end{aligned} $$ $$\ab{b}$$ $$f=465\ut{N},$$ $$ \begin{aligned} \KE_b&=400g-3720\\ &=202.66\ut{J}\\ &\approx 203\ut{J}\\ \end{aligned} $$