I need help on Physics question?

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 80.0km/h, 12 min at 100 km/h, and 45 min at 40 km/h, and spends 15 min eating lunch and buying gas.

A) determine the average speed for the trip

B)Determine the distance between the initial and final cities along this route.

Any ideas? Can you explain how you got the answers?

Thanks

Answer 1

average speed is total distance divided by total time.

We need to calculate distances piece by piece

1. 80 km/hr x 0.5 hr = 40 km

2. 100 km/hr x 12/60 hr = 20 km

3. 40 km/hr x 3/4 hr = 30 km

4. 0 km

total distance = 90 km

total time = 30 + 12 + 45  + 15 = 102 minutes

Average speed = 90 km/102 min x 60 min/hr = 52.9 km/hr

total distance = 90 km

.

Answer 2

The answer (without giving it away, since this looks like a homework question) is that

A)  The average speed is the average distance per time, right, so it's:

total distance traveled

--------------------------------

total time taken

so, find the total distance, and the total time and you have it!

B)  You had to find the total distance to do part A.