The centre of mass of a body

Two particle of masses $1\,kg$ and $3\,kg$ have position vector $2\hat i + 3\hat j + 4\hat k$ and $ - 2\hat i + 3\hat j - 4\hat k$ respectively. The centre of mass has a position vector

Three particles of masses $50\, g$, $100\, g$ and $150\, g$ are placed at the vertices of an equilateral triangle of side $1\, m$ (as shown in the figure). The $(x, y)$ coordinates of the centre of mass will be

$A$ man weighing $80\, kg$ is standing at the centre of a flat boat and he is $20\, m$ from the shore. He walks $8\, m$ on the boat towards the shore and then halts. The boat weight $200\, kg$. ........ $m$ far is he from the shore at the end of this time.

From a uniform disk of radius $R$, a circular hole of radius $R/2$ is cut out. The centre of the hole is at $R/2$ from the centre of the original disc. Locate the centre of gravity of the resulting flat body.

Mention the position of centre of mass of particles of equal mass.