Instantaneous Velocity Car Problem

1. Sep 18, 2010

mopar969

A car is stopped at a traffic light. It then travels along a straight road so that its distance from the light is given by x(t)= bt^2 -ct^3, where b = 2.40m/s^2 and c = 0.120 m/s^3. How do you calculate the average velocity of the car for the time interval t=0 to t=10.

I think that maybe I need to take the derivative of the equation but then what please help!

2. Sep 18, 2010

collinsmark

Hello mopar969,
If you only need to find the average velocity, simply calculate the total distance traveled, divided by the time it takes to get there.

3. Sep 18, 2010

mopar969

Thank you. I cant believe that it was that simple. I was thinking instantaneous velocity that is why I was thinking about taking its derivative.
However, the question has another part to it that I am stuck on it says:

4. Sep 18, 2010

You're searching the time t when the velocity is 0.

x(t)= bt^2 -ct^3, this finds the displacement as a function of time. You'll need another equation (related to this one) to find the velocity as a function of time.

5. Sep 18, 2010

mopar969

Would I need the derivative of the displacement function?

6. Sep 18, 2010

Yes that would give you the velocity.

7. Sep 18, 2010

mopar969

My next problem is how do I get t by itself?

8. Sep 18, 2010

mopar969

Never mind I realized that I could use the quadratic formula.