Question

PLEASE HELP In this graph of displacement vs time http://i.imgur.com/uoHGw.png
A. the acceleration and velocity are always positive
B. the velocity is first negative and then positive
C. the acceleration is first negative and then positive
D. the acceleration is positive, and the velocity changes from negative to positive

Answer 1

I think its d

Answer 2

Try to picture each of the 4 options in your mind. What would the graphs look like?

Answer 3

Think about velocity first, because that's an easier concept to grasp.

Answer 4

You have two choices here. You can look at the graph and intuitively determine what is going on. Or, you can systematically look at points along the curve and calculate the rates of change.

Answer 5

@geoffb , can d actually exist?

Answer 6

I thinj it b

Answer 7

@chocokatlove Yes, that would be like a car going backward but braking, who comes to a stop then speeds up forward.

Answer 8

The stop would need to be instantaneous—probably not the best example—but the theory is possible.

Answer 9

@tryder Can you explain your reasoning for B?

Answer 10

@geoffb The velocity is positive and increasing. First I pick D and they told me its wrong. So I pick B

Answer 11

Okay, good. You have the right answer (velocity is indeed positive and increasing, which is the same as saying acceleration is positive), but the answer (of the four) you chose is not correct.

Answer 12

They drew the graph purposely to try to trick you. The fact that you start at a negative *displacement* does not have anything to do with the value of velocity.

If I give New York a displacement value of 0, and drive to LA, I presumably have a positive velocity the entire way (assume I never stop).

If instead, I call Denver displacement 0, I am obviously starting at a negative displacement in New York. That doesn't mean my velocity ever becomes negative because of it.