Two racquetballs, each having a mass of 144 g, are placed in a glass jar as shown in in the figure below. Their centers lie on a straight line that makes a 45° angle with the horizontal.

To help explain the situation, I will need the figure you mentioned. However, based on the description you provided, I can still provide some helpful information.

Since the centers of the two racquetballs lie on a straight line that makes a 45° angle with the horizontal, we can infer that the racquetballs were likely placed vertically in the jar. This means that the jar is oriented with its opening at the bottom.

You mentioned that each racquetball has a mass of 144 g. If there are no external forces acting on the system of racquetballs in the jar, then the net force on the system must be zero.

Since the downward force due to the weight of the racquetballs is balanced by the normal force exerted by the jar, the net vertical force is zero. Therefore, the vertical acceleration is zero.

However, there can still be a horizontal acceleration if there are other forces acting on the system. Without more information or the figure you mentioned, it is difficult to determine the specific forces and calculate the resulting acceleration.

If you could provide more details or the figure, I would be able to give a more accurate explanation of the situation.