## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

(a) $t_1 = \frac{d}{v} = \frac{50~mi}{40~mph}$ $t_1 = 1.25~hours$ $t_2 = \frac{d}{v} = \frac{50~mi}{60~mph}$ $t_2 = 0.833~hours$ total time = $t_1+t_2$ total time = $1.25~h+0.833~h$ total time = $2.08~hours$ average speed = $\frac{100~mi}{2.08~hours}$ average speed = 48.1 mph (b) Let $t$ be the time spent driving at each speed. total distance = $40t+60t$ total time = $2t$ average speed = $\frac{40t+60t}{2t}$ average speed = 50 mph