Which is true about atoms?
a. atoms have no mass
b. atoms are mostly empty space
c. most of the space in an atom is taken up by the nucleus?

What are similarities and differences of reflection, refraction, diffraction and absorption?

Coal contains energy. a. light b. kinetic c. chemical d. mechanical

Determine the time it takes for a satellite to orbit the earth in a circular "near-earth" orbit. the definition of "near-earth" orbit is one which is at a height above the surface of the earth which is small compared to the radius of the earth, so that you may take the acceleration due to gravity as essentially the same as that on the surface. does your result depend on the mass of the satellite?