# Two dimensional kinematics

1. Oct 9, 2009

### indietro

1. The problem statement, all variables and given/known data
a flying saucer manueverign with a constant acceleration is observed with the positions and velocities shown below. what is the saucer's acceleration?

2. Relevant equations
a = $$\Delta$$v / t

3. The attempt at a solution
so a time is not given.. is there another way to find acceleration?
** actually if someone knows a site that gives a clear and concise tutorial on two-dimensional kinematics that would be great :). I know there is one attached to this site.. but i do better with actual examples and more visual.

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2. Oct 9, 2009

### tiny-tim

Hi indietro!

(I can't see the picture yet, but …)

The standard trick for finding dv/dt from v and s without involving t is to use the chain rule …

dv/dt = dv/dx dx/dt = v dv/dx

3. Oct 9, 2009

### indietro

oo ok for the picture it is a x-y graph that shows a point at (0.0) with a vertical vector (200$$\hat{j}$$ m/s) and a second point at (2000, 1000) with a south-east vector (200$$\hat{i}$$ - 100$$\hat{j}$$ m/s)

for the chain rule: is the v the final velocity?

4. Oct 9, 2009

v = dx/dt

5. Oct 9, 2009

### indietro

so i have a question: for an x-y graph showing the trajectory, what does $$\vec{r}$$ (starts at origin and goes to a point on the trajectory) tell me? the velocity at that point? or does it only tell me the direction of velocity at that point?

6. Oct 9, 2009

### indietro

sorry but im really confused as how to relate an xy-graph, a vx graph, a vy graph and acceleration. Like what does each tell me, how can i find position after a certain time, how can i find acceleration?

7. Oct 10, 2009

### tiny-tim

Hi indietro!

(just got up :zzz: …)
r only tells you the position, and the direction of the tangent of the trajectory tells you the direction of the velocity.
Why are you using a graph? Does the question tell you to?

If it doesn't, then forget graphs, and just use equations.

8. Oct 10, 2009

### indietro

yes the question gives me all the information in the form of an vx graph and vy graph ...:(

9. Oct 10, 2009

### tiny-tim

hmm … I still can't see your picture.

I'll have to wait until I can see it.

(I've reported it, so hopefully it'll come up soon )

10. Oct 10, 2009

### tiny-tim

oooh, I see it now! :tongue2:​

ok, that isn't a graph (a graph would be a continuous curve) …

it's just a diagram, defining the two velocities in a picture instead of in words.

So you don't have to use a "graph method" …

just write the velocities as 200j and 200i - 100j, and carry on from there.