7-5 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} d&=35.0\ut{cm}\\ F_1&=5.00\ut{N}\\ F_2&=1.00\ut{N}\\ F_3&=6.00\ut{N}\\ \theta&=60.0\degree\\ m&=2.4\ut{kg}\\ K_0&=0 \end{cases} $$ $$\ab{a}$$ $$\Sigma \vec F = 0 \Harr \Delta \vec v=0,$$ $$\Sigma F_y=0$$ $$ \begin{aligned} \Sigma F_x &= F_1-F_2+F_3\cos\theta\\ &=7\ut{N} \end{aligned} $$ $$ \begin{aligned} W&=\vec F \cdot \vec d,\\ &=\frac{49}{20}\ut{J}\\ &=2.45\ut{J}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} K_1&=K_0+\Delta K\\ \frac{1}{2}m{v_1}^2&=K_0+W\\ \end{aligned} $$ $$ \begin{aligned} v_1&=\sqrt{\frac{2W}{m}}\\ &=\frac{7}{2\sqrt6}\ut{m/s}\\ &\approx 1.4288690166235207\ut{m/s}\\ &\approx 1.43\ut{m/s}\\ \end{aligned} $$