A layer of oil, with a refractive index of 1.40798, 0.98966 mm thick, floats on water. (a) Light of vacuum wavelength 632.800 nm, emitted by a stabilized He-Ne laser, is reflected at normal incidence by the oil. How many wavelengths are contained in the light wave passing back and forth through the oil?

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.