# Avg Speed

## Homework Statement

A car travels to home from school. For the first 100km it travels 100km/h and for the rest of trip travels 50km/hr and completes the trip in 1 hr and 42 min. Calculate the avg speed for the ENTIRE trip.

## Homework Equations

Average Speed=∑i|d/Δttotal

## The Attempt at a Solution

It's asking for the entire trip so we assume it comes back home.

In this case is avg speed = 0 because the displacement was 0.

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It looks like an incomplete text. Is this the actual text or a "summary"?

It looks like an incomplete text. Is this the actual text or a "summary"?

I'm just wondering if it is correct

Aha, you modified the text.
Now it makes sense. And you can calculate the average speed.
The trip is exactly what they say: from school to home.
Calculate the total distance traveled and divide by the total time.
It may some room for interpretation when they say "completes the trip in 1 h and 42 min".
He did the first 100 km (in 1h) and then it takes another 1h 42min to finish the trip?
Or he completed the whole trip in 1 h and 42 min, which will leave 42 min for the portion traveled with 50 km/h.

so what I said is wrong? We have to assume they came from home to school. The actual question bolds the words "entire trip"

PhanthomJay
Homework Helper
Gold Member
so what I said is wrong? We have to assume they came from home to school. The actual question bolds the words "entire trip"
No, this is not a valid assumption. No info is given for the home to school trip. And besides, average velocity and average speed are not the same when traveling round trip. By the ENTIRE trip it means both sections of the one way trip from school to home.

so then the avg speed would be 75 km/h

Average speed is not the average of the two speeds. You need to use the formula you wrote yourself. Total distance/total time.

Average speed is not the average of the two speeds. You need to use the formula you wrote yourself. Total distance/total time.

Forgive me guys, this was a test question I'm just going off memory. But a friend told me that it said the person drove from home.

So then the entire trip would be to the school and back.

If this is the case, then is the avg speed 0m/s?

PhanthomJay