Unknown distances, constant speed, average velocity

[oceanbunny]

Homework Statement

A car travels along a straight line at a constant speed of 48.5 mi/h for distance d and then another distance d in the same direction at another constant speed. The average velocity for the entire trip is 30.5mi/h.

a) What is the constant speed with which the car moved during the second distance d?

Homework Equations

I know that speed = distance/ delta time, and that velocity = displacement/ delta time

The Attempt at a Solution

The only formula that I thought might help was Xfinal = Xinitial + (1/2)(Vxinitial + Vxfinal)time but then I decided that it was a dumb formula to use and now I'm stuck :/ I can't seem to relate the constant speed and average velocity to each other the right way..

Please help!

 

[PhanthomJay]

What is the equation for average velocity as a function of displacement and time? You are going to have to calculate the total time of the trip by summing the time it takes for each part of the trip at the different speeds. Some algebraic manipulation is involved.