7-14 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} F_a&=20.0\ut{N}\\ m&=2.00\ut{kg}\\ \theta&=25.0\degree\\ d&=0.700\ut{m}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$\ab{a}$$ $$W=\vec F \cdot \vec S,$$ $$ \begin{aligned} W_{F_a}&=F_a d \cos\theta\\ &\approx 12.688309018513099\ut{J}\\ &\approx 12.7\ut{J}\\ \\ W_{mg}&=mg d \cos(90\degree+\theta)\\ &\approx -5.802257127099202\ut{J}\\ &\approx -5.80\ut{J}\\ \\ W_{F_N}&=F_N d \cos90\degree\\ &=0 \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} K&=K_0+\Sigma W\\ \frac{1}{2}mv^2&=W_{F_a}+W_{mg}+W_{F_N}\\ \end{aligned} $$ $$ \begin{aligned} v&=\sqrt\frac{2(W_{F_a}+W_{mg})}{m}\\ &\approx 2.6241287871241945\ut{m/s}\\ &\approx 2.62\ut{m/s}\\ \end{aligned} $$