Which force provides the centripetal force in the case of rotation of an electron round the nucleus of an atom?

Does the acceleration of a body remain constant when it revolves along a circular path with uniform angular velocity?

Two bodies of masses $m_1$ and $m_2$ move in circles of radii $r_1$ and $r_2$ respectively, if they complete the circles in equal time, the ratio of their angular velocities is

A pellet of mass $1 \mathrm{g}$ is moving with an angular velocity of $1 \mathrm{rad}/\mathrm{s}$ along a circle of $1$ metre. The centrifugal force is

A small coin is placed on a whirling table. The coin just begins to slip when it is placed $4 \mathrm{cm}$ from the centre of the table. If the table rotates with double the angular speed, at what distance from the centre of the table should the coin be placed so that it just starts slipping?