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 (c): the crossarm will remain perpendicular to the track, as seen in an mpeg video by clicking your mouse on the photograph at the right below. Note that the crossarm does not rotate in this case until "the hand" stops the cart by applying a force near the center of the cart.
In both of these cases, the situation illustrates "gravitational mass." The acceleration of each mass results from the component of gravitational force exerted on the mass in the direction of the motion. The situation here is similar to the free fall of two unequal masses dropped simultaneously.
