Students performed several trials using the laboratory setup shown.
Students were also given this hypothesis: If friction increases, then the
rolling distance of a marble will decrease. What should be changed to
best test this hypothesis?
Classroom Investigation

The roughness of the surface should be varied by the students tp test the hypothesis in the best possible way.

Explanation:

As the hypothesis stated the relation between roughness of the surface and the distance covered by the marble, students first need to find the independent variable among these two. The independent variable will be the one which will not depend on the result of the other variable. But there will be change in the dependent variable on changing the independent variable.

So here the independent variable is the roughness of the surface as per the hypothesis. And the dependent variable will be distance covered by the marble.

So the students should vary the independent variable and check for desired changes in the dependent variable for confirmation of hypothesis.

Thus, the roughness of the surface should be varied by the students tp test the hypothesis in the best possible way.

0.11 m/s and 0.28 m/s should be correct