# VELOCITY-TIME GRAPH

1. Jul 17, 2004

### bayan

How do you calculate the instantanius velocity of an object from a Velocity-Time graph?

2. Jul 17, 2004

### jcsd

The instaneous velocity of the object described in the graph at a partycular time t, is simply it's velcoity at that time. In other words you don't have to do any calculus (like you weould have to do if you wished to find the average vellcoity over a certain time) just read the value from the graph.

3. Jul 17, 2004

### HallsofIvy

Are you sure this is what you meant? As jcsd pointed out, if you really have a "velocity- time" graph, then the instantaneous velocity is just the "y" value of the graph at time t.

If you have a "position-time" graph, then the velocity is the slope of the tangent line at the point.

If you have a "velocity-time" graph, then the acceleration is the slope of the tangent line.

4. Jul 17, 2004

### bayan

sorry i asked the wrong question.

How do you calculate the Acceleration at a given time?

5. Jul 17, 2004

### bayan

and also the tangent line is curved *the train accelerates at diffrent acceleratio*

6. Jul 17, 2004

### Didd

accleration: velocity per unit time or V/t. It is just as is as this one.

7. Jul 17, 2004

### jcsd

a = dv/dt

i.e. differentiate

8. Jul 17, 2004

### bayan

can you explain abit more please

9. Jul 17, 2004

### jcsd

If you only have the graph find the gradient of the grpah at that particular point, if you have the equation differentiate v with respect to t.

10. Jul 17, 2004

### HallsofIvy

As I said before: if you have a "Velocity-time" graph, draw a tangent to the curve at the given value of t and find its slope.