Name the force which provides the centripetal force in the following case:

A stone tied at one end of a string is being whirled.

Name the force which provides the centripetal force in the following case:

An electron is revolving round a nucleus.

When a car takes a turn round a curve, a passenger sitting in a car tends to slide. To which side does the passenger slide? Why?

What is the necessity of banking the road? Which factors the angle of banking depends upon?

Two cars having masses $m_1$ and $m_2$ are moving in circles of radii $r_1$ and $r_2$ respectively. If they go once round their circles in equal time, find the ratio of their angular speeds.

Define centripetal force and establish an expression for the same.