Final answer:
X-rays are powerful enough to pass through some substances but not others due to the density of the materials and the energy of the x-ray photons. They excel at detecting breaks in bones and imaging structures that differ in density.
Step-by-step explanation:
X-rays are powerful enough to pass through some substances, like skin and muscle, but not others, like bone, due to the density of the materials and the energy of the x-ray photons. The denser the material, the fewer x-ray photons can pass through, resulting in a darker shadow. X-rays excel at detecting breaks in bones and imaging structures that differ in density from surrounding material, such as tumors.