5-60 할리데이 11판 솔루션 일반물리학

$$\begin{cases} m&=0.20\ut{kg}\\ \vec v_0&=2.0\i\ut{m/s}\\ t&=0.50\ut{s}\\ \end{cases}$$ $$\ab{a}$$ $$\vec v_1=-5.0\i\ut{m/s}$$ $$\begin{aligned} \vec F&=m\vec a\\ &=m\frac{\vec v_1-\vec v_0}{t}\\ &=(0.2)\frac{-5\i-2\i}{0.5}\\ &=-\frac{14}{5}\i\\ F&=2.8\ut{N},\text{West} \end{aligned}$$ $$\ab{b}$$ $$\vec v_1=-5.0\j\ut{m/s}$$ $$\begin{aligned} \vec F&=m\vec a\\ &=m\frac{\vec v_1-\vec v_0}{t}\\ &=(0.2)\frac{-5\j-2\i}{0.5}\\ &=-0.8\i-2\j\\ \end{aligned}$$ $$\begin{aligned} F&=\sqrt{0.8^2+2^2}\\ &=\frac{2}{5}\sqrt{29}\ut{N}\\ &\approx 2.1540659228538015\ut{N}\\ &\approx 2.2\ut{N}\\ \end{aligned}$$ $$\begin{aligned} \theta &=\tan^{-1}\frac{-2}{-0.8}\\ &\approx -1.9513027039072615\ut{rad}\\ &\approx -2.0\ut{rad}\\ \end{aligned}$$