Answer the following :- Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet’s velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why ?

A comet orbits the sun in a highly elliptical orbit. Does the comet have a constant:- linear speed,

A comet orbits the sun in a highly elliptical orbit. Does the comet have a constant:- angular momentum,

A comet orbits the sun in a highly elliptical orbit. Does the comet have a constant:- angular speed,

A comet orbits the sun in a highly elliptical orbit. Does the comet have a constant:- kinetic energy,

A comet orbits the sun in a highly elliptical orbit. Does the comet have a constant:- potential energy,

A comet orbits the sun in a highly elliptical orbit. Does the comet have a constant:- total energy throughout its orbit? Neglect any mass loss of the comet when it comes very close to the Sun.

What is the amount of work done by sun's gravitational force if earth is rotating in almost circular orbit?

Answer the following :- If you compare the gravitational force on the earth due to the sun to that due to the moon, you would find that the Sun’s pull is greater than the moon’s pull. (you can check this yourself using the data available in the succeeding exercises). However, the tidal effect of the moon’s pull is greater than the tidal effect of sun. Why ?

A rain drop of radius 2 mm falls from a height of 500 nr above the ground. It falls with decreasing acceleration (due to viscous resistance of the air) until at half its original height, it attains its maximum (terminal) speed, and moves with uniform speed thereafter. What is the work done by the gravitational force on the drop in the first and second half of its journey ? What is the work done by the resistive force in the entire journey if its speed on reaching the ground is 10 m s^-1 ?