Final answer:
True. Stress marks on the edge of a radial crack are always perpendicular to the edge of the surface on which the impact force originated.
Step-by-step explanation:
True. Stress marks on the edge of a radial crack are always perpendicular to the edge of the surface on which the impact force originated. This is because stress is a result of the force acting perpendicular to the surface, causing deformation. When a crack occurs, the stress lines will be perpendicular to the edge of the crack as it is the direction in which the force is applied.