# Help with average speed/instantaneous speed!

1. Sep 23, 2007

### Bensky

Help with average speed/instantaneous speed! :(

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

1. EDIT: Figured this one out, now I just need to know about the 2nd question about instantaneous speed.
2. What is its instantaneous speed at t = 20 s?

2. Relevant equations

v= change in x/change in t

3. The attempt at a solution

I have no idea how to do this. My textbook doesn't really cover this section well, and I'm just starting out in Physics.
I did v=2/20 and came out with .1, but I think it's wrong.

Last edited: Sep 23, 2007
2. Sep 23, 2007

### FedEx

Is it average speed or average velocity.As it is a displacement versus time graph.

3. Sep 23, 2007

### Bensky

Average speed. That's where I'm confused. Why would they give me that type of graph?

4. Sep 23, 2007

### Sourabh N

Average speed is the area of the graph divided by the time.

5. Sep 23, 2007

### Bensky

Ok, well I figured out the average speed by doing d/t I think. Either way, it told me I was right, so now I just have the instantaneous speed problem that I don't understand. D:

Last edited: Sep 23, 2007
6. Sep 23, 2007

### Sourabh N

instanteneous speed is defined as the tangent to the curve at that point(time).

7. Sep 23, 2007

### Bensky

So I would use the slope formula to find it?

8. Sep 23, 2007

### Sourabh N

Ya. How did u get the area under the curve.