# Help with instantaneous velocity

1. Sep 6, 2004

### ramin86

I was given the following graph:

http://www.webassign.net/pse/p2-03.gif

I must find the instantaneous velocity at T=1.4

The formula for instantaneous velocity is delta x/delta t as t approaches zero. However, I'm still not sure how to work this problem. Please help

2. Sep 6, 2004

### e(ho0n3

Find the equation for x(t) in the interval t = [0,2]. You should know the velocity by then.

3. Sep 6, 2004

### Chronos

The formula you gave is for instantaneous acceleration, not velocity. So I will assume you are looking for instantaneous acceleration.
You will note the graph is a straight line from 0 - 2 seconds which means the acceleration is constant. The instantaneous acceleration is therefore the same as the average acceleration over that interval.

4. Sep 6, 2004

### ramin86

No, its instantaneous velocity that I'm looking for. I thought instantaneous acceleration is the change in velocity over the change in time.

5. Sep 6, 2004

### needhelpperson

HOWEVER though, the graph does not show change in velocity over change in time. It's simply distance vs time. Besides, Ramin gave the right formula, distance over change in time. i think you should ignore chrono's comments Ramin......

Since it is a straight line though, the velocity is not changing, so you can just find the instantaneous velocity by finding the slope of the 0-2 second interval(since t = 1.4 has the same velocity as that interval)

Last edited: Sep 6, 2004
6. Sep 6, 2004

### Chronos

My bad, you are correct, dx/dt. Make a table x1, t1, x2, t2. x1 and t1 will always be 0,0. x2 and t2 will be per the graph. solve for dx/dt at t2 = 1.4 seconds. Hint dx is always x2 - x1 and dt is always t2 - t1