Creating a Position vs. Time Graph for a Moving Car

[swede5670]

Homework Statement

A car is moving down the street toward you and speeding up. Create a corresponding position versus time graph.

Homework Equations

Well its just a graph so...none?

The Attempt at a Solution

I submitted a graph that started at the origin and had a curved, positive slope. For some reason that was called incorrect and I'm not sure how else the graph would look. It cannot be a straight line because that would imply that the object had uniform motion

 

[LowlyPion]

Homework Statement

A car is moving down the street toward you and speeding up. Create a corresponding position versus time graph.

Homework Equations

Well its just a graph so...none?

The Attempt at a Solution

I submitted a graph that started at the origin and had a curved, positive slope. For some reason that was called incorrect and I'm not sure how else the graph would look. It cannot be a straight line because that would imply that the object had uniform motion

What you describe is a diminishing position relationship. Perhaps the desired answer is one that starts slowly at the distance away the car is and describes a downward parabolic arc that ends at T = road kill?

 

[Wecht]

How did you shape it? If it's curved like the letter 'J', I don't see what's wrong with that. But if it's shaped like the letter 'r', that means it decelerating.
Do you know for sure that the curve is wrong, or did you maybe label the axes incorrectly, or not put a title for the graph?

 

[LowlyPion]

How did you shape it? If it's curved like the letter 'J', I don't see what's wrong with that. But if it's shaped like the letter 'r', that means it decelerating.
Do you know for sure that the curve is wrong, or did you maybe label the axes incorrectly, or not put a title for the graph?

I didn't label anything. You should try and set up axes where the initial condition at T= 0 is the distance away. And goes to smaller distance faster the closer it gets to T = impact.

 

[tiny-tim]

Hi swede5670!

A car is moving down the street toward you and speeding up. Create a corresponding position versus time graph.
…
I submitted a graph that started at the origin and had a curved, positive slope. For some reason that was called incorrect and I'm not sure how else the graph would look. It cannot be a straight line because that would imply that the object had uniform motion

Why the origin?

Isn't that where you are?

 

[Wecht]

Hm I don't think so, TinyTim. The origin should be the car's position at t = 0. Since it's accelerating towards him, he can't be at the point where the car is, because then it wouldn't be accelerating towards him.

 

[tiny-tim]

Hm I don't think so, TinyTim. The origin should be the car's position at t = 0. Since it's accelerating towards him, he can't be at the point where the car is, because then it wouldn't be accelerating towards him.

Hi Wecht!

I think the origin should be the observer's position.

If the car was falling out of the sky, would the origin still be the car's position at t = 0?

 

[Wecht]

I'm not sure I'm understanding you correctly. The question says the car is coming down the street towards you; I'm pretty sure it's safe to assume that it's not falling out of the sky.

 

[Sakha]

From what I understood it should be something like ..mm the part of the circle at the I quadrant, or a ¯| curve.

 

[Wecht]

I think you guys are making this more complicated than it really is.

 

[Wecht]

Wait, is this supposed to be an x-position vs time graph of the car, or what?

 

[Sakha]

Create a corresponding position versus time graph.

Yup, its a X vs t graph

 

[Wecht]

So if it's an x vs t graph of the car, it doesn't matter where the person is. Why is TinyTim suggesting that the car is falling out of the sky? And also that the origin is the position of the person?