Two particles A and B are moving in a uniform circular motion in concentric circles of radii $r_A and r_B$ with speeds $v_A and v_B$ respectively. Their time periods of rotation are the same. The ratio of angular speed of A  to that of B will be:

1. 1: 1

2. $r_A : r_B$

3. $v_A : v_B$

4. $r_B : r_A$

A particle starting from rest moves in a circle of radius 'r'. It attains a velocity of $v_0$ m/s on completion of n rounds. Its angular acceleration will be:

1. $\frac{v_0}{n} rad/s^2$

2. $\frac{v_0^2}{2{\mathrm{\pi nr}}^2} rad/s^2$

3. $\frac{v_o^2}{4{\mathrm{\pi nr}}^2} rad/s^2$

4. $\frac{v_0^2}{4\mathrm{\pi nr}} rad/s^2$