Question

A person travels by car from one city to another with different constant speeds between pairs of cities. She drives for 30.0 min at 80.0 km/h, 45.0 min at 40 km/h and 12.0 min at 100 km/h, and spends 15.0 min eating lunch and buying gas. Determine the average sped for the trip. Determine the difference between the intial citties along the route.

Answer 1

Answer:

Average speed of the trip = 52.9 km/h

Distance between initial pairs of cities (start to end) = 70.0 km

Explanation:

Since distance = speed × time

If she drives 30.0 min at 80.0 km/h

Distance covered = (30/60) × 80 = 40.0 km

Again she drives 45.0 min at 40 km/h

Distance covered = (45/60) × 40 = 30.0 km

Again she drives 12.0 min at 100 km/h

Distance covered = (12/60) × 100 = 20.0 km

Total distance covered =  40.0 + 30.0 + 20.0

                                       = 90.0 km

Total time spent = 30.0 + 45.0 + 12.0 +15.0

                           = 102 min

Average speed for the trip = Total distance covered/total time spent

                                             = 90/(102/60)

                                             = 52.9 km/h

Distance between initial cities will be between the start of one city to the end of another

Between the first pairs = 40.0 + 30.0 = 70.0 km

Between the second pairs = 30.0 + 20.0 = 50.0 km