7-3 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} A:\text{Time 0 to 1}\\ B:\text{Time 1 to 2}\\ C:\text{Time 2 to 3}\\ \end{cases} $$ $$ \begin{cases} v&=0.60\ut{m/s}\\ m&=3.5\ut{kg} \end{cases} $$ $$ \begin{cases} \theta_A&=10\degree\\ S_A&=4.2\ut{m}\\ \end{cases} $$ $$ \begin{cases} \theta_B&=0\\ S_B&=2.0\ut{m}\\ \end{cases} $$ $$ \begin{cases} \theta_C&=-10\degree\\ S_C&=4.2\ut{m}\\ \end{cases} $$ $$W=\vec F \cdot \vec d,$$ $$ \begin{aligned} P&=\dxt{W}\\ &=\dt{(\vec F \cdot \vec d)}\\ &=\dt{(mgh)}\\ &=mg\dt{(h)}\\ &=mg\dt{(S\sin\theta)}\\ &=mgv\sin\theta\\ \end{aligned} $$ $$\ab{a}$$ $$ \begin{aligned} P_a&=mgv\sin\theta\\ &\approx 3.576104493186545\ut{W}\\ &\approx 3.6\ut{W}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} P_a&=mgv\sin\theta\\ &=0\ut{W} \end{aligned} $$ $$\ab{c}$$ $$ \begin{aligned} P_a&=mgv\sin\theta\\ &\approx -3.576104493186545\ut{W}\\ &\approx -3.6\ut{W}\\ \end{aligned} $$