8-79 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m&=3.6\ut{kg}\\ y&=3.8\ut{m}\\ g&=9.80665\ut{m/s^2}\\ \end{cases} $$ $$ \put \begin{cases} \KE : \text{Kinetic Energy}\\ \GE : \text{Gravitational Potential Energy}\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \GE&=mgy\\ &=\frac{342g}{25}\\ &=134.154972\ut{J}\\ &\approx 1.3\times10^2\ut{J}\\ \end{aligned} $$ $$\ab{b}$$ $$\Sigma \Delta E=0,$$ $$ \begin{aligned} \KE&=\GE\\ &=134.154972\ut{J}\\ &\approx 1.3\times10^2\ut{J}\\ \end{aligned} $$ $$\ab{c}$$ $$ \begin{aligned} \KE&=\frac{1}{2}mv^2\\ v&=\sqrt\frac{2\KE}{m}\\ &=\sqrt\frac{38g}{5}\\ &\approx 8.633107204245757\ut{m/s}\\ &\approx 8.6\ut{m/s}\\ \end{aligned} $$