# Velocity Vs Time Conceptual Question

• neon612
In summary, the problem involves two cars traveling on parallel lanes on a two-lane road. The cars' motions are represented by a velocity versus time graph. The student has 5 attempts to answer a question before it is counted wrong, and is on their last attempt. The graph shows points A through E, and after each attempt, the feedback stated that the location of the cars is unknown and all that is known is their velocities at points A, B, C, and E. The cars have the same velocity at point D, car 1 stops at point B, and car 2 stops at point E. When thinking of the cars as traveling on an east-west road, car 1 is traveling west and slowing down until it

#### neon612

This is homework help, but I think all I need to learn is how to read a VT graph properly. My professor uses MasteringPhysics.com and this is one of the questions from the site. The way it works is: the student has 5 attempts to answer a question before it is counted wrong and I'm down to my last attempt. I'm hoping I've already figured out the right answer and I just need to make sure that what I think is the right answer actually is.

After each attempt it gave me some feedback saying "The location of the cars are unknown at this time. All that is known is their velocities." And that was for points A, B, C, and E.

## Homework Statement

Two cars travel on the parallel lanes of a two lane road. The cars' motions are represented by the velocity versus time graph. Answer each of the questions with reference to the lettered times (A through E) marked on the graph. (graph attached)

http://img703.imageshack.us/img703/633/1011351.jpg [Broken]

At which of the lettered times, if any, do the two cars pass?

## The Attempt at a Solution

From my textbook and searching the net I've been able to figure out:

The two cars have the same velocity at point D
Car 1 stops at point B
Car 2 stops at point E

If I think about it as a east-west road, I come up with:
Car 1 is traveling west and slowing down until it gets to point B. Then it accelerates, heading east.

Car 2 is traveling west and slowing down until half a graph square before A. Then it speeds up heading east until point C, when it starts slowing down until point E. It stops at point E, and speeds up heading west.

I know the area under the curve will tell me the displacement. But how does that work if I'm not given any numbers to work with?

So, I guess the answer I keep coming up with is that the problem doesn't have enough information to figure an exact position. (To put it in the wording from Mastering Physics "Cannot be Determined")

Last edited by a moderator:
Ummm ... where's the graph?

Sorry, I thought I had attached it to the opening post.

Actually for answering this, i need to know do the 2 cars start from same point or matbe initial distance b/w them

cupid.callin said:
Actually for answering this, i need to know do the 2 cars start from same point or matbe initial distance b/w them

Actually, this is all the information I am given to solve the problem. There are other parts to answer (but I've already answered them):

When does car 1 stop? -> At B
when does car 2 stop? -> At E
And when do they have the same velocity -> at D