2-47 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} v_1&=65\ut{mi/h}\\ v_2&=70\ut{mi/h}\\ S &= 700\ut{km}\\ \end{cases} $$ $$ \begin{cases} 1\ut{mile}&=5280\ut{ft}\\ 1\ut{ft}&=12\ut{in}\\ 1\ut{in}&=2.54\ut{cm}\\ \therefore 1\ut{mile}&=1.609344\ut{km} \end{cases} $$ $$ \begin{aligned} \Delta t &= t_1-t_2\\ &=\frac{S}{v_1}-\frac{S}{v_2}\\ &=S\(\frac{1}{v_1}-\frac{1}{v_2}\)\\ &=(700\ut{km})\(\frac{1}{65\ut{mi/h}}-\frac{1}{70\ut{mi/h}}\)\\ &=\frac{700\ut{km}}{910\ut{mi/h}}\\ &=\frac{700\ut{km}}{910\ut{mi/h}}\cdot\frac{1\ut{mile}}{1.609344\ut{km}}\\ &=\frac{78125}{163449}\ut{h}\approx 0.4779778401825646\ut{h}\\ &=\frac{1562500}{54483}\ut{min}\\ &\approx 28.67867041095387\ut{min}\\ &\approx 29\ut{min} \end{aligned} $$