Distance and speed

1. Sep 8, 2009

AKsamantha

1. The problem statement, all variables and given/known data

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

2. Relevant equations
I used (avg)s=distance/time

3. The attempt at a solution
I got 6.2 km/h which I know is way off.

2. Sep 8, 2009

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

3. Sep 8, 2009

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.