The pendulum bob is dropped from point a and swings to point c. the pendulum bob swings back and forth but eventually it stops. why?
a) all the potential energy is converted to kinetic energy.
b) the external energy source is less than the friction force.
c) there cannot be continued motion without an external energy source.
d) all the kinetic energy is converted to potential energy or energy of position.

Antireflective coatings on solar cells are often made by applying a thin film of silicon nitride (sinx), which has an index of refractive of 1.2, on the top of the silicon solar cell, which has a refractive index of about 3.5. however, the sun emits radiation of various wavelengths which the solar cell absorbs, and the antireflective coating can only absolutely minimize the reflection of one of these wavelengths. the coating thickness is chosen to reduce the reflection of green/yellow light (e = 2.2 ev), which is the most intense color in the solar spectrum (shown below). which of the following coatings would minimize reflection of green/yellow light? the answer is 820 nm how? what is the angular width of the central maximum of an electron traveling at 2 x 108 m/s going through a single slit of width 1 mm.