Two particles $A$ and $B$ initially at rest move towards each other under a mutual force of attraction. At the instant when the speed of $A$ is $v$ and the speed of $B$ is $2v$, the speed of centre of mass of the system is
$Zero$
$v$
$1.5\ v$
$3\ v$
Four masses are fixed on a massless rod as shown in Fig. The moment of inertia about the axis $P$ is about ....... $kg-m^2$
A circular disk of moment of inertia $I_t$ is rotating in a horizontal plane, about its symmetry axis, with a constant angular speed ${\omega _i}$. Another disk of moment of inertia $I_b$ is dropped coaxially onto the rotating disk. Initially the second disk has zero angular speed. Eventually both the disks rotate with a constant angular speed ${\omega _f}$. The energy lost by the initially rotating disc to friction is
A ring of radius $4a$ is rigidly fixed in vertical position on a table. A small disc of mass $m$ and radius $a$ is released as shown in the fig. When the disc rolls down, without slipping, to the lowest point of the ring, then its speed will be
If a solid sphere is rolling, the ratio of its rotational energy to the total kinetic energy is given by
$A$ bob of mass $m$ is attached to a string whose other end is tied to a light vertical rod as shown in figure. The bob is swinging in horizontal plane with constant angular speed $\omega$. The vertical rod is supported on a block of mass $M$ which is placed on a rough surface. What is minimum friction coefficient between ground and block for which block does not slip ?