12. List the features of the photoelectric effect that cannot be explained by the wave nature of light? What is Einstein's postulate to explain the photoelectric effect?

10. Several objects (a hoop, a solid cylinder, a solid sphere, and a thin spherical shell) roll, without slipping down an incline of vertical height H, all starting from rest at the same moment. In addition a box slides down without friction. In what order do they reach the bottom of the incline?