5-52 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m&=0.400\ut{kg}\\ x(t\ut{s})&=(-13.00+12.0t+3.00t^2-2.00t^3)\i\ut{m}\\ t&=1.20\ut{s} \end{cases} $$ $$ \begin{aligned} \Sigma F&=ma\\ &=m\dxtt{x}\\ &=m\cdot\dtt(-13+12t+3t^2-2t^3)\i\\ &=m(6-12t)\i\\ &=\frac{12}{5}(1-2t)\i \end{aligned} $$ $$ \begin{aligned} F(1.2)&=-\frac{84}{25}\i\ut{N}\\ &=-3.36\i\ut{N}\\ \end{aligned} $$