Question

A motorist travels for 3.0 h at 80 km/h and 2.0 h at 100 km/h. What is her average speed for the trip?

Answer 1

Answer:

The motorist average speed for the trip is 88 km/h

Explanation:

In order to know her average speed, we have to refer to the following ecuation:

<V> (average speed) = $\frac{Vfinal+Vinital}{2}$

So, according to that, we know that the motorist has been having a speed of 80km/h during 3 hours, and a speed of 100 km/h during 2 hours. It means that her speed during all the travel is 5 hours.

Then, we have to affect the 5 hours to the inicial and final speed as follows:

First, at 80 km/h, she travels during 2 hours so:

3h*80km/h= 240 km

And then, at 100 km/h:

2h*100km/h= 200 km

Which leads us to:

initial speed: 240 km/ 5 h= 48 km/h

and final speed of: 200 km/ 5 h= 40 km/h

Then, the average speed is:

<V> = 48 km/h + 40 km/h = 88 km/h

Answer 2

3x80=240
2x100=200
240+200/5=88 k/hr
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