6-26 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} mg&=556\ut{N}\\ \mu_s&=0.68\\ \mu_k&=0.56\\ \end{cases} $$ $$ \begin{aligned} f_s&=\mu_sF_N=\mu_smg\\ &=\frac{9452}{25}\ut{N}\\ &=378.08\ut{N}\\ \end{aligned} $$ $$ \begin{aligned} f_k&=\mu_kF_N=\mu_kmg\\ &=\frac{7784}{25}\ut{N}\\ &=311.36\ut{N}\\ \end{aligned} $$ $$\ab{a}$$ $$ \begin{aligned} F_a&=250\ut{N}\lt f_s,\\ &\therefore \text{Stop}\\ f&=F_a=250\ut{N}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} F_b&=365\ut{N}\lt f_s,\\ &\therefore \text{Stop}\\ f&=F_b=365\ut{N}\\ \end{aligned} $$ $$\ab{c}$$ $$ \begin{aligned} F&=420\ut{N}\gt f_s,\\ &\therefore \text{Move}\\ f&=f_k=311.36\ut{N}\\ &\approx 3.1\times10^2\ut{N} \end{aligned} $$ $$\ab{d}$$ $$ \begin{aligned} F&=556\ut{N}\gt f_s,\\ &\therefore \text{Move}\\ f&=f_k=311.36\ut{N}\\ &\approx 3.1\times10^2\ut{N} \end{aligned} $$ $$\ab{e}$$ $$\text{c,d}$$