Calculating Average Speed of a Road Trip

[toothpick09]

A person travels by car from one city to another with different constant speeds between pairs of cities. She drives for 15.0 min at 65.0 km/h, 20.0 min at 75.0 km/h and 60.0 min at 40.0 km/h, and spends 15.0 min eating lunch and buying gas.

Determine the average speed for the trip.

I know average speed is total distance/total time but I am confused as to how to get the total distance. For the total time I added 15+20+60+15 and got 110 minutes. Would displacement play a part in this problem?

 

[cepheid]

See this thread:

https://www.physicsforums.com/showthread.php?t=171509

Don't double post!

 

[m2003]

To calculate the average speed for this road trip, you can use the formula: average speed = total distance / total time. In this case, the total time is 110 minutes.

To find the total distance, you can use the formula: distance = speed x time. So for the first leg of the trip, the distance would be 65 km/h x 15 min = 16.25 km. For the second leg, the distance would be 75 km/h x 20 min = 25 km. And for the third leg, the distance would be 40 km/h x 60 min = 40 km. The total distance for the trip would be 16.25 km + 25 km + 40 km = 81.25 km.

Therefore, the average speed for the trip would be 81.25 km / 110 min = 0.74 km/min, or approximately 44.4 km/h. Displacement does not play a role in this calculation, as average speed is only dependent on the total distance and total time, not the direction of travel.