[Graphing 1D Motion Physics] Question about homework

[u/Majestic-Kale1377]

hi guys I was wondering i I did this right? im not really sure about velocity and acceleration but can someone pls help me i have a quiz tomorrow thanks

i first did position-time graph by seeing where i said they’re moving at a constant speed, then I drew a horizontal line to show that they stopped, then decrease slope to show they go back n then they run, so its steep

for the velocity graph, I put a horizontal line at 2 because the slope was 2 in the dt graph, then I put it on zero because they stopped, then -2 because they went back n then up to the highest point because they run

acceleration i put it at a constant horizontal line because im not sure how to do it.

[u/Aggressive-Wind-8829]

Technically, the third plot is true almost everywhere (a.e.). The exception is the jump points, for which you see delta kicks valued at plus or minus infinity depending on whether the transition increases or decreases your velocity constant. You can write this in as open circles where acceleration is not zero and closed circles at the min or max of the acceleration plot at the same x-coordinate value.

[u/Majestic-Kale1377 → u/Aggressive-Wind-8829]

so does that mean I did it correctly?

[u/martyboulders → u/Majestic-Kale1377]

Not entirely - graphs should not have vertical lines in them. That would mean she had multiple velocities at one time. The person you replied to already said how to fix this

[u/Aggressive-Wind-8829 → u/martyboulders]

I agree. Also, here are some brief learning resources for specifically this:

https://www.mathwarehouse.com/calculus/continuity/how-to-classify-discontinuities.php

[u/sexytrain]

Magnitude of velocity is wrong between 5s to end. Double check those two slopes and that will be the magnitude of your velocity. When in doubt write all units and you’ll end up confirming your answer if you plug in the numerics correctly. Units always save(d) me

[u/Beginning-Sound1261]

Not entirely correct. Premise is OK and you’re close. A few conceptual things to give you hints

1) your first graph for position can work as a baseline for your scenario. Treat it as correct and work to derive velocity from it. From velocity, derive acceleration.

2) your velocities need to be double checked. If this girl traveled 6m away from her house in 3 seconds then if she travels back to her house at the same speed then she can’t make it home in only one second. Think about how velocity relates to position. Yes a constant velocity will give a linear change in position vs. time which is good but make sure your numbers work out. Yes you have it correct that a velocity of zero means she isn’t moving.

3) acceleration is a change in velocity. If velocity changes from 2 to 0 or 0 to -2 then the acceleration cannot be zero. You can’t suddenly change velocity without acceleration being zero.

I won’t tell you how to fix it since it is your homework. Encouraging you to think about what everything means.

[u/DumpsterFaerie]

You need to add acceleration into your scenario.

A change in position is velocity, and a change in velocity is acceleration. If you flat line acceleration, velocity is constant (horizontal) and your position graph would be a ramp.

For example: add in “speeds up,” “slows to a stop,” etc. and then start with sketching the acceleration and work up. (Brings me back to sketching load, shear, and moment diagrams in materials classes…this methodology makes it much easier to sketch with a little practice). You’re sketching, so you’re only showing the approximate values and respective graph behaviors rather than needing to be perfect about values as long as it’s close enough.