Why do you think people had a hard time accepting the idea of gravity as a force that keeps planets in their orbits?

Find v(t), given acceleration a(t)=7j and initial velocity v(0)=k

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.

Suppose a comet has an orbital period of 309.1 years around the sun. what is it’s average distance from the sun?