Separation of Motion of a system of particles into motion of the centre of mass and motion about the centre of mass:
(i) Show p=p_{i}^{\prime}+m_{i} V Where p_{i} is the momentum of the i^{\text {th }} particle (of mass \left.m_{i}\right) and p_{i}=m_{i} v_{i}^{t} . Note v_{i}^{\prime} is the velocity of the \mathrm{i}^{\mathrm{ith}} particle with respect to the centre of mass.Also, verify using the definition of the centre of mass that \Sigma p_{i}=0
(ii) Prove that \mathrm{K}=\mathrm{K}^{\prime}+1 / 2 \mathrm{MV}^{2} Where K is the total kinetic energy of the system of particles, K^{\prime} is the total kinetic energy of the system when the particle velocities are taken relative to the center of mass and \mathrm{MV}^{2} / 2 is the kinetic energy of the translation of the system as a whole.
Separation of Motion of a system of particles into motion of the centre of mass and motion about the centre of mass:
(i) Show p=p_{i}^{\prime}+m_{i} V Where p_{i} is the momentum of the i^{\text {th }} particle (of mass \left.m_{i}\right) and p_{i}=m_{i} v_{i}^{t} . Note v_{i}^{\prime} is the velocity of the \mathrm{i}^{\mathrm{ith}} particle with respect to the centre of mass.Also, verify using the definition of the centre of mass that \Sigma p_{i}=0
(ii) Prove that \mathrm{K}=\mathrm{K}^{\prime}+1 / 2 \mathrm{MV}^{2} Where K is the total kinetic energy of the system of particles, K^{\prime} is the total kinetic energy of the system when the particle velocities are taken relative to the center of mass and \mathrm{MV}^{2} / 2 is the kinetic energy of the translation of the system as a whole.

i)Here \vec{r}_{i}=\vec{r}_{i}+\vec{R}+R \ldots also, \vec{V}_{i}=\vec{V}_{i}+\vec{V} \ldots \ldots .

Where \vec{r}_{i}^{\overrightarrow{3}} and \vec{v}_{i}^{\overrightarrow{3}} denote the radius vector and velocity of the \mathrm{i}^{\text {th }} particle refers to the new origin as the centre of mass \mathrm{O}‘, and \vec{V} is the velocity of the centre of mass with respect to O.

Momentum of \mathrm{th}^{\text {th }} particle can be calculated as,

\vec{p}^{\prime}=m_{i} \vec{V}_{i}

=m_{i}\left(\vec{V}_{i}+\vec{V}\right)

[ From equation (1)]

Or, \vec{P}=m_{i} \vec{V}+\vec{P}_{i}

(ii) Kinetic energy of system of particles can be calculated as

\mathrm{K}=\frac{1}{2} \sum m_{i} V_{i}^{2}

=\frac{1}{2} \sum m_{i} \vec{V}_{i} \cdot \vec{V}_{i}

=\frac{1}{2} \sum m_{i}\left(\vec{V}_{i}+\vec{V}\right)\left(\vec{V}_{i}+\vec{V}\right)

=\frac{1}{2} \sum m_{i}\left(\overrightarrow{V_{i}}^{2}+\overrightarrow{V^{2}}+2 \vec{V}_{i}{ }_{i} \vec{V}\right)

=\frac{1}{2} \sum m_{i} V_{i}^{, 2}+\frac{1}{2} \sum m_{i} V^{2}+\sum m_{i} \vec{V}_{i}^{\prime} \vec{V}

=1 / 2 M V^{2}+K

Where \mathrm{M} or \sum m_{i} is the total mass of the system.

\mathrm{K}^{\prime}=\frac{1}{2} \sum m_{i} V_{i}^{\prime 2}

= kinetic energy of motion about the centre of mass.

Or, 1 / 2 M v^{2}= kinetic energy of motion of centre of mass.(Proved)