The answer to the first question is (c): the crossarm will remain perpendicular to the track, as seen in an mpeg video by clicking your mouse on the photograph at the left below.
The answer to the second question is (a): the crossarm will rotate clockwise as viewed from above, as seen in an mpeg video by clicking your mouse on the photograph at the right below.
These cases are similar to the situations encountered in the previous question. In both of these cases, the situation illustrates "inertial mass." The acceleration of each mass, and thus the rotation of the arm, results from the moment of inertia of that mass about the pivot point, compared to that of the other mass, during the acceleration of the cart. The greater mass, having greater moment of inertia about the pivot point, will be harder to accelerate, so that mass will rotate toward the rear of the cart as it accelerates. This is equivalent to the acceleration of the arm that would occur if there were a gravitational field pulling backward on the inertial mass cart and its attachments.
