Let us assume that our galaxy consists of `2.5×10^11` stars each of one solar mass. How long will a star at a distance of 50,000 ly from the galactic center take to complete on revolution? Take the diameter of the Milky way to be `10^5ly`.

The number density of free electrons in a copper conductor estimated is 8.5x10^28m^(-3) . How long does an electron take in drifting from one enf of a wire 3.0m long to its other end? The area of cross-section of the wire is 2.0x10^(-8)m^2 and it is carrying a current of 3.0A.

A rocket is fired from the earth towards the Sun. At what distance from the earth's center is the gravitational force on the rocket zero? Mass of the Sun=2×10^30kg , Mass of the earth=6×10^24kg . Neglect the effect of the other planets etc. ( Orbital radius=1.5×10^11m )