7-50 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \vec F&=3x\i+6\j\ut{N}\\ \vec r_i&=2\i+3\j\ut{m}\\ \vec r_f&=-4\i-3\j\ut{m}\\ \end{cases} $$ $$ \begin{aligned} \Delta r &= (-4\i-3\j)-(2\i+3\j)\\ &=-6\i-6\j\ut{m} \end{aligned} $$ $$W=\vec F \cdot \vec S,$$ $$ \begin{aligned} W&=(3x\i+6\j)\cdot(-6\i-6\j)\\ &=-18x-36\ut{J} \end{aligned} $$