Determine the average speed for the car trip

In summary, the person's trip was broken up into different segments with constant speeds. By calculating the distance traveled in each segment and adding them up, the total distance was found to be 81.25 km. However, to find the average speed, which is 0.7386 km/min, the total distance must be divided by the total time of 110 minutes. To convert this to km/h, the units must be carried, resulting in an average speed of 44.45 km/h for the trip.
  • #1
toothpick09
12
0

Homework Statement


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.


Homework Equations


Average Speed = total distance/total time


The Attempt at a Solution


(65+75+80)/(15+20+60+15)=1.64 which isn't logical. I don't understand how to compute the total distance?
 
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  • #2
Well, the trip is naturally broken up into segments. So don't worry about calculating the total distance if that confuses you. Calculate the distance traveled in each segment and then add them up. For example, first she travels for 15 min at 65 km/h. Okay, how far did she travel in the 15 minutes?
 
  • #3
I took each time divided by 60 to give me hours then multiplied that number by the km/h. Added them up and got 81.25. What am I doing wrong?
 
  • #4
toothpick09 said:
I took each time divided by 60 to give me hours then multiplied that number by the km/h. Added them up and got 81.25. What am I doing wrong?

What are the units? If you included the units you would see that this is not an average speed. What you got is the total distance. To find the average speed, you must still divide by the total time (in hours if you want the average speed in km/hr). Don't forget to include the 15 minutes break time.
 
  • #5
So after getting 81.25 which would be my total distance I divide by the total time which would be 110. This gives me .738636. This doesn't seem logical but is what I am doing correct?
 
  • #6
You really would make your life a lot easier if you just carry the units in your calculations.

The total distance traveled is 81.25km as you said

The total time taken for the trip is 110min just as you said

So you have [tex]\frac{81.25}{110} km/min[/tex]

Can you convert that to km/h ?
 

1. How do you calculate average speed for a car trip?

To calculate average speed for a car trip, you need to divide the total distance traveled by the total time taken. The formula is: average speed = total distance / total time.

2. What units are typically used for measuring average speed?

The most common units for measuring average speed are miles per hour (mph) or kilometers per hour (km/h). However, other units such as meters per second (m/s) or feet per second (ft/s) can also be used.

3. Is average speed the same as instantaneous speed?

No, average speed and instantaneous speed are not the same. Average speed is the total distance traveled divided by the total time taken, while instantaneous speed is the speed at a specific moment in time. Average speed gives an overall picture of the trip, while instantaneous speed is more specific to a particular point on the trip.

4. How does the type of terrain affect the average speed for a car trip?

The type of terrain can greatly affect the average speed for a car trip. For example, driving on a smooth highway with no traffic will likely result in a higher average speed compared to driving on a winding mountain road with heavy traffic. Uphill terrain will also result in a slower average speed compared to downhill terrain.

5. Can average speed be greater than the maximum speed limit?

Yes, it is possible for the average speed for a car trip to be greater than the maximum speed limit. This can happen if the car travels at a high speed for a short period of time, but spends most of the trip at a lower speed. However, it is important to always follow the maximum speed limit to ensure safety while driving.

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