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# How to find speed from distance time graphs (Physics AS) Watch

1. Can someone help me and show me how i can answer this physics AS question. Its about finding speed from distance time graphs, i dont know how to do it so will be greatful for showing me.
I have added an attahment of the question so PLEASE someone help.

Attached Images

2. speed is just the gradient of a distance time graph. if you need help remembering just think about the units.

so at t = 4

a rough estimate of the gradient is 10.... you need to work this out properly though
3. (Original post by didgeridoo12uk)
speed is just the gradient of a distance time graph. if you need help remembering just think about the units.

so at t = 4

a rough estimate of the gradient is 10.... you need to work this out properly though

Sorry i have no idea how to work it out.. If u can kindly show/ explain to me i will be very greatful! Any could u explain what u mean by remembering units. But please explain how u work it out anyway!

Thanks
4. Differentiate and put in 4?
5. (Original post by soup)
Differentiate and put in 4?
How do you differentiate a graph which has no corresponding function?

Draw a tangent to the curve where x = 4, and then use m = (change in y) / /(change in x)
6. (Original post by mujahid_e3)
Sorry i have no idea how to work it out.. If u can kindly show/ explain to me i will be very greatful! Any could u explain what u mean by remembering units. But please explain how u work it out anyway!

Thanks
draw a tangent to the curve at t =4. work out the gradient of this line (you must be able to do this, if not look on the internet)

and in regards to units.

speed is in units of m/s
distance is in units of m
time is in units of s

so to get speed you need to divide some numbers involving distance by some involving time.
7. Here's an example done for you.
Your question is very similar, the only difference is that the slope of my graph is negative and yours will be positive, that is, sloping up from left to right.
The slope of my graph is 5m / 7.5s
this equals 0.67 m/s
8. (Original post by soup)
Differentiate and put in 4?
There is no equation to differentiate!
9. (Original post by mujahid_e3)
There is no equation to differentiate!
Yes ok I know that now!
10. (Original post by mujahid_e3)
There is no equation to differentiate!

stonebridge told you waht to do
11. Why is everyone over complicating things? No need for differentiation, drawing a tangent or w/e.
The question asks what the speed is at 4.0s.

So just take the value of the distance at 4s, and divide the one by the other.
So you get s = 16/4 , which i'm sure you can work out.

(You can draw a tangent, but there is no need.)
Why is everyone over complicating things? No need for differentiation, drawing a tangent or w/e.
The question asks what the speed is at 4.0s.

So just take the value of the distance at 4s, and divide the one by the other.
So you get s = 16/4 , which i'm sure you can work out.

(You can draw a tangent, but there is no need.)
People are not over complicating it.

Speed is only distance/time for uniform velocity.
The graph, because it is a curve, is not uniform velocity.
You cannot calculate velocity by just dividing the distance by the time from a point on the graph. You have to draw the tangent and measure the slope.

It's not an option.

And thanks hazbaz.
Yes, I did explain what to do but it seems to have gone unnoticed.
13. (Original post by Stonebridge)
People are not over complicating it.

Speed is only distance/time for uniform velocity.
The graph, because it is a curve, is not uniform velocity.
You cannot calculate velocity by just dividing the distance by the time from a point on the graph. You have to draw the tangent and measure the slope.

It's not an option.

And thanks hazbaz.
Yes, I did explain what to do but it seems to have gone unnoticed.
Indeed. Yep it does I think people need to be more observant :P.
14. (Original post by Stonebridge)
Here's an example done for you.
Your question is very similar, the only difference is that the slope of my graph is negative and yours will be positive, that is, sloping up from left to right.
The slope of my graph is 5m / 7.5s
this equals 0.67 m/s
Thanks will try to follow this!
15. (Original post by Stonebridge)
People are not over complicating it.

Speed is only distance/time for uniform velocity.
The graph, because it is a curve, is not uniform velocity.
You cannot calculate velocity by just dividing the distance by the time from a point on the graph. You have to draw the tangent and measure the slope.
Silly me. You're right. I was over-simplifying lol.
16. Are you serious? Draw a tangent at 4 seconds and find the gradient. (Distance/time) Honestly...
17. (Original post by Antstien)
Are you serious? Draw a tangent at 4 seconds and find the gradient. (Distance/time) Honestly...
18. (Original post by mujahid_e3)
Well you had been told several times what to do...
19. (Original post by hazbaz)
Well you had been told several times what to do...
Yes i have reaslised it and applied it?? So whats your point!!

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