circular motion Questions

Which of the following statements is false for a particle moving in a circle with a constant angular speed?

A particle of mass $M$ and charge $Q$ moving with velocity $\vec{v}$ describes a circular path of radius $R$ when subjected to a uniform transverse magnetic field of induction $B$. The work done by the field when the particle completes one full circle is:

A point $P$ moves in counter-clockwise direction on a circular path of radius $20\text{m}$. The movement of '$P$ ' is such that it sweeps out a length $s=t^3+5$, where $s$ is in metres and $t$ is in seconds. The acceleration of '$P$ ' when $t=2\text{s}$ is nearly:

For a particle in uniform circular motion the acceleration $\vec{a}$ at a point $P(R,\theta )$ on the circle of radius $R$ is (here $\theta$ is measured from the $x$ -axis):

Two cars of masses $m_1$ and $m_2$ are moving in circles of radii $r_1$ and $r_2$, respectively. Their speeds are such that they make complete circles in the same time $t$. The ratio of their centripetal acceleration is: