6-20 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \theta&=35\degree\\ S&=2.1\ut{m}\\ t&=4.0\ut{s}\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{cases} \Sigma F_x &= 0\\ \Sigma F_y &= 0\\ \end{cases} $$ $$ \begin{cases} \mu_sF_N-mg\sin\theta &= 0\\ F_N-mg\cos\theta &= 0\\ \end{cases} $$ $$\mu_smg\cos\theta-mg\sin\theta=0$$ $$ \begin{aligned} \mu_s&=\tan\theta\\ &=\tan35\degree\\ &\approx 0.7002075382097097\\ &\approx 0.70\\ \end{aligned} $$ $$\ab{b}$$ $$S=v_0t+\frac{1}{2}at^2,$$ $$ \begin{aligned} S&=(0)t+\frac{1}{2}at^2\\ a&=\frac{21}{80}\ut{m/s^2} \end{aligned} $$ $$\Sigma \vec F = m\vec a,$$ $$ \begin{aligned} ma&=mg\sin\theta-\mu_kF_N\\ &=mg\sin\theta-\mu_kmg\cos\theta\\ \mu_k&=\tan\theta-\frac{a}{g\cos\theta}\\ &\approx 0.6675303926452323\\ &\approx 0.67\\ \end{aligned} $$