velocity vs time graph!!!!


by npena29
Tags: graph, time, velocity
npena29
npena29 is offline
#1
Sep10-10, 09:05 PM
P: 9
hola everyone! i have posted this before but not sure it went through....i would appeciated it is someone would help me with it.

The world record in the 100m dash set by usain "lighting" bolt at the 2009 world championships, is 9.58s. draw a velocity-vs-time graph of his run, taking into account the following information:
1. acceleration is not constant.
2. the maximum instantaneous speed that a human being can reach is 13.8m/s
3. a 100 m runner accelerates up to his peak speed early in the race, sustains it as long as he can, but is already slowing down in the late stages of the race.

the graph should be drawn carefully enough that its possible to see that the area under the curve represents the 100m distance run.


the graph i have, i labeled the x-axis as m/s for the 13.8...and i converted Bolts speed 9.58 as 10.4 m/s2 and the yaxis as meters for the 100m dash. ok from there, whats the next step? how would i graph it??
Phys.Org News Partner Science news on Phys.org
SensaBubble: It's a bubble, but not as we know it (w/ video)
The hemihelix: Scientists discover a new shape using rubber bands (w/ video)
Microbes provide insights into evolution of human language
collinsmark
collinsmark is offline
#2
Sep10-10, 09:12 PM
HW Helper
PF Gold
collinsmark's Avatar
P: 1,848
Hello9 npena29,

Welcome to Physics Forums!
Quote Quote by npena29 View Post
The world record in the 100m dash set by usain "lighting" bolt at the 2009 world championships, is 9.58s. draw a velocity-vs-time graph of his run, taking into account the following information:

[...snip...]

the graph i have, i labeled the x-axis as m/s for the 13.8...and i converted Bolts speed 9.58 as 10.4 m/s2 and the yaxis as meters for the 100m dash. ok from there, whats the next step? how would i graph it??
Make the x-axis time (units of seconds [Hint: 0 sec represents the start of the race. The race ends in 9.58 sec])

Make the y-axis velocity (units m/s).

[Edit: Whenever you are asked to make a plot of "this" vs. "that", it is implied "this" is the y-axis and "that" is the x-axis.]
npena29
npena29 is offline
#3
Sep11-10, 12:47 AM
P: 9
ok...so what happens to the 100m dash?

collinsmark
collinsmark is offline
#4
Sep11-10, 01:16 AM
HW Helper
PF Gold
collinsmark's Avatar
P: 1,848

velocity vs time graph!!!!


Quote Quote by npena29 View Post
ok...so what happens to the 100m dash?
It's the area under the curve!

It sounds like you get to create the curve on your own. If you want to keep it simple, you might wish to combine a right triangle and a trapezoid (plus maybe a rectangle too), but I'm guessing you're free to be creative. Choose the dimensions carefully such that the maximum height is what you desire (Hint: that 13.8m/s should fit right in here somewhere), and the overall area is 100 m.
npena29
npena29 is offline
#5
Sep11-10, 02:57 PM
P: 9
i have attached the graph..does it look something like that?
Attached Thumbnails
CCF09112010_00000.jpg  
collinsmark
collinsmark is offline
#6
Sep12-10, 02:24 AM
HW Helper
PF Gold
collinsmark's Avatar
P: 1,848
Quote Quote by npena29 View Post
i have attached the graph..does it look something like that?
The x-axis looks pretty good.

The y-axis needs some work. The way you have drawn it, starting from zero, the first tick is 4 ms, implying that there is 4 m/s per tick. But the next 4 ticks go from 4 to 12 m/s (a difference of 8 m/s); that's only 2 m/s per tick. Then the last two ticks only span 1.8 m/s. Redo the y-axis, making all the ticks evenly spaced.

To the right you have the equation

[tex] \frac{100 \ \mathrm{m}}{9.58 \ \mathrm{sec}} = 10.44 \ \mathrm{m/s}, [/tex]

which is good to know. That is Usain "Lighting" Bolt's average speed. So when it comes time to make your plot, you know that his instantaneous speed will sometimes be above that number, sometimes below.

Then you have 9.58 s = 10.44 m/s. I have no idea what that means.

Eventually you will need to make the actual plot. Like I mentioned before your life will be a lot easier if you stick to using straight lines. To start, you'll need to make a straight line from 0 up to some speed less than or equal to 13.8 m/s (but you should probably try to stay a little less than that). From there you need a couple more lines, but you can figure these out.

Like the problem statement said, take care to ensure the total area under the curve represents the 100 m. So you should probably do a few calculations first. Make sure you know the area formulas for a triangle, a square, and a trapezoid. Choose the dimensions of these shapes carefully, so their total area is 100 m.

(If you're wondering why area is in units of meters here, look at the axes of the graph. One dimension, length, is seconds [s]. The other dimension, height, is meters per second [m/s], so the units of the area, length times height, [s][m/s] = [m].)
npena29
npena29 is offline
#7
Sep21-10, 12:28 PM
P: 9
i got it! thank you very much


Register to reply

Related Discussions
how to draw distance-time graph from velocity-time graph? General Physics 2
how to do velocity-time graph to distance graph/acceleration to velocity graph? Classical Physics 1
How do I calculate speed in a velocity-time graph? Displacement-time graph? Introductory Physics Homework 1
velocity vs time graph to distance vs time graph Introductory Physics Homework 8
How to get a Fnet vs. time graph from a velocity vs time graph. Introductory Physics Homework 1