DASI-P - Dot Diagram Selected Response

What important physics idea is this question targeting?

This will examine if students can determine an equation to calculate position if they know the acceleration on the object, and then accurately represent that calculation on the diagram. (I/V)
This targets a few ideas, but primarily it’s about the independence of motion in perpendicular directions — the object keeps moving north at a constant speed while it accelerates east. (C)
This question is targeting whether or not students can use dot (or strobe) representations of motion to determine position, speed and acceleration. (V)

Which answer best describes what student A's response indicates about their physics understanding?

This student is thinking intuitively about the physics but is not consistently applying the correct equations in order to determine the position of the object. They likely have trouble going between two different kinds of representation (algebraic and graphical). (I/V)
This student is struggling with two ideas. First, they don't have a strong understanding of the difference between acceleration and velocity. Second, they no longer have the object moving north, which suggests that they think the eastward force will cause the object to go east and stop going north. That is, they are not treating the two directions independently. (C)
The student is clearly engaged with the problem and is reasoning through the ideas. They show the object turning and speeding up and and explain their ideas. They could benefit from more clarity and precision in their work. (V)

Which of the following options would best support Student A in being able to correctly respond to this question?

I would have one group of students create the dot diagram for the object if no force is acting on it (so it keeps moving north at the same speed). And then another group would only think about the eastward motion and how to show that acceleration. After ensuring they had different representations for constant speed and constant acceleration, we would discuss how to combine the two to see that the eastward motion is independent of the northward motion. (C)
I would put our equations of motion on the board for students and have them work in pairs to determine the position of the object over time. Since there is no acceleration given, I would ask students to suggest a reasonable acceleration to use in these equations of motion. We could then accurately plot the data. (I)
I would have this student compare their diagram to a peer’s diagram and see what differences they notice. (V)

Which answer best describes what student B's response indicates about their physics understanding?

While the student correctly identifies an equation of motion to use for constant acceleration, they start time at t = 0 without recognizing that the object has already been traveling at a constant speed for 3 seconds. They need support in understanding how to determine the values for variables in their equations. (I)
They make a reasonable assumption for acceleration and apply it consistently to calculate eastward displacement over time, however, they fail to consider how the motion to the north will impact the object's trajectory. (C)
The student has trouble moving between graphical representations and algebra. (V)

Which of the following options would best support Student B in being able to correctly respond to this question?

I would acknowledge their strong use of equations of motion to determine the eastward velocity and then ask them to use those same equations for the northward velocity. (C)
I would ask the student to create a table with time and position on it; hopefully this would clarify which values to assign to which variables. We could then compare this with other students' work if they are still confused. (I)
I would ask the student to check their reasoning with a peer and then draw a consensus diagram on their whiteboard. (V)