Final answer:
In a collision between two trucks that stick together, if the combined speed is more than half the original speed of the moving truck, the moving truck had less mass or contents. If the combined speed is less than half, the stationary truck had more mass or contents. This is described by the conservation of momentum.
Step-by-step explanation:
When two trucks that look the same on the outside collide and stick together, the resulting motion can tell us something about the masses or contents of the trucks. In physics, this type of collision is addressed by the law of conservation of momentum, which states that the total momentum of a system remains constant if no external forces act on it.
(a) If the trucks stick together and move off at more than half the original speed of the moving truck, we can infer that the moving truck must have had a lower mass or less contents than the stationary truck. Since momentum (product of mass and velocity) is conserved, a higher final speed suggests lower mass for the moving truck.
(b) Conversely, if the trucks stick together and move off at less than half the original speed of the moving truck, this implies that the stationary truck was more massive or had more contents. A lower final speed compared to the initial speed of the moving truck indicates that the combined mass (after collision) has increased significantly due to the mass of the stationary truck.