Average speed for 80km at 100 km/h and 50km at 75 km/h

[AKsamantha]

Homework Statement

A mortorist travels 80km at 100 km/h, and 50 km at 75 km/h. WHat is the average speed for the trip?

Homework Equations

I used (avg)s=distance/time

The Attempt at a Solution

I got 6.2 km/h which I know is way off.

 

[fatra2]

It's a good first step to realize that your answer is not terribly realistic.

I believe you have the right equation. The average speed is: d/t. What is the total distance travel (d=?)? The little trick will be to find out how long it took the motorist to travel this distance (t=?)?

Cheers

 

[Jebus_Chris]

$$v_{avg}=\frac{\Delta x }{\Delta t}$$
Find how far it travels in part one and add that to how far it travels in trip 2. And do the same for t.