5-45 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m&=4.0\ut{kg}\\ \vec x(t\ut{s})&=3.0+4.0t+ct^2-3t^3\ut{m}\\ \vec F(2.0\ut{s})&=-48\ut{N} \end{cases} $$ $$ \begin{aligned} \vec a&=\dxtt{\vec x}\\ &=\dtt(3.0+4.0t+ct^2-3t^3)\\ &=2c-18t\\ \end{aligned} $$ $$ \begin{aligned} F&=ma\\ &=8(c-9t)\\ F(2)&=8 (c-18)=-48,\\ c&=12\ut{m/s^2} \end{aligned} $$