Two point masses of $0.3\, kg$ and $0.7\, kg$ are fixed at the ends of a rod of length $1.4\, m$ and of negligible mass. The rod is set rotating about an axis perpendicular to its length with a uniform angular speed. The point on the rod through which the axis should pass in order that the work required for rotation of the rod is minimum is located at a distance of

To find the centre of mass of rigid body why it is not possible to know$\sum {{m_i}\overrightarrow {{r_i}} } $ for all the particles ? 

Write the difference between centre of gravity and centre of mass of a body?

In general form what are the coordinates of centre of mass of a rigid body.

In the figure shown find out the distance of centre of mass of a system of a uniform circular plate of radius $3R$ from $O$ in which a hole of radius $R$ is cut whose centre is at $2R$ distance from centre of large circular plate

In the figure one fourth part of $a$ uniform disc of radius $R$ is shown. The distance of the centre of mass of this object from centre $‘O’$ is: