## Physics: Principles with Applications (7th Edition)

The total distance is 500 km. The displacement is zero; the endpoint is the same as the beginning point. Average speed: use distance traveled and the total time. Calculate the time in the first leg by dividing the distance by the constant speed. t1 = (250 km)(95 km/h) = 2.632 hr. Keep a few extra significant figures for now. Do the same for the return trip. t2 = (250 km)(55 km/h) = 4.545 hr. The total time, including lunch, is 8.177 hr. $$\frac{500 km}{8.177 h} = 61 km/h$$ The displacement is zero so the average velocity is zero.