the graph is tied to the reading

here is the reading for the question

students in a physics class observing the race note that each runner maintains the same acceleration from the start ofthe 8.0 second interval until they each reach the finish line where each of the runners slows to a stop. Two students inthe class make the following claims about the runners’ accelerations from the start of the 8.0 second interval until bothrunners are at rest.

Student 1:“Runner A has a positive acceleration until reaching the finish line and then a negative acceleration aftercrossing the finish line in order to “undo” all of the positive velocity she gained. Since Runner B neverhad any positive acceleration, she doesn’t need any negative acceleration to slow to a stop; heracceleration will be zero the whole time.”

Student 2:“But negative values mean away south in this case – how could runner A be turning around? I think bothrunners must have positive accelerations the whole time since they are always moving north.”

For part (c), do not simple repeat the students’ arguments in your answers.

here are the questions:

i.Which aspects of student 1’s reasoning, if any, are correct? Explain your answer.

ii.Which aspects of student 1’s reasoning, if any, are incorrect? Explain your answer.

iii.Which aspects of student 2’s reasoning, if any, are correct? Explain your answer.

iv.Which aspects of student 2’s reasoning, if any, are incorrect? Explain your answer

THANK YOU THANK YOU THANK YOU

i. Positive acceleration increases velocity. Negative acceleration decreases velocity. runner A sped up until the finish line and then slowed to a stop.

ii. Zero a acceleration implies a constant, unchanging velocity not a zero velocity. runner B achieved some velocity prior to 8s and is moving and must slow down to reach a stop.

iii. None. No aspects of this reasoning are correct. Everything she says is wrong. See iv for what/why.

iv. The sign on acceleration denotes the direction of *change in velocity* not change in direction. The sign on velocity can denote change in direction but only “forward” or “reverse” along a particular path. Cardinal direction is not indicated, generally, by the sign on velocity. It may correspond to North/South situationally but it is not an built-in feature of velocity and its sign. For example, if you are traveling with positive velocity and turn left to continue your journey you still have a positive velocity in the new direction. In fact, if you turn left again, traveling in the opposite direction as the one you started with your velocity would still be positive… in the new direction. The velocity relative to original direction could be said to be negative but that would be a confusing way to describe a journey. Maybe if you stopped the vehicle and moved in reverse, you could meaningfully say velocity was negative.