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Center Of Mass MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

Syllabus

Quick Facts

Center of mass is considered one the most difficult concept.
17 Questions around this concept.

Solve by difficulty

EASY

Consider a two-particle system with particles having masses m₁ and m_{2 .} If the first particle is pushed towards the centre of mass through a distance d, by what distance should the second particle be moved, so as to keep the centre of mass at the same position?

$d$

$\frac{m_{2}}{m_{1}}d$

$\frac{m_{1}}{m_{1}+m_{2}}d$

$\frac{m_{1}}{m_{2}}d$

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Consider the system of two particles having masses m₁ and m₂. If the particle of mass m₁ is pushed towards the centre of mass particles through a distance d, by what distance would the particle mass m₂ move to keep the mass centre of particles at the original position?

$\frac{m_1 d}{m_1+m_2}$

$\frac{m_1 d}{m_2}$

$\frac{m_2}{m_1} d$

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Concepts Covered - 1

Center of mass

Definition-

Centre of mass of a body is defined as a single point at which the whole mass of the body or system is imagined to be concentrated and all external forces are applied there.
It is the point where if a force is applied it moves in the direction of the force without rotating.

x, y, & z coordinates of centre of mass

For a system of N discrete particles

$$
\begin{aligned}
x_{c m} & =\frac{m_1 x_1+m_2 x_2 \ldots \ldots \ldots}{m_1+m_2 \ldots \ldots} \\
y_{c m} & =\frac{m_1 y_1+m_2 y_2+m_3 y_3 \ldots \ldots \ldots}{m_1+m_2+m_3 \ldots \ldots} \\
z_{c m} & =\frac{m_1 z_1+m_2 z_2+m_3 z_3 \ldots \ldots \cdots}{m_1+m_2+m_3 \ldots \ldots}
\end{aligned}
$$

Where $m_1 m_2$. $\qquad$ are the mass of each particle $x_1, x_2$ $\qquad$ $y_1, y_2$ $\qquad$ $z_1, z_2$ are respectively $x_1$ $y, \& z$ coordinates of particles.
- It is the unique point where the weighted relative position of the distributed mass sums to zero.
- Centre of Mass of a Continuous Distribution

$$
x_{c m}=\frac{\int x d m}{\int d m}, \quad y_{c m}=\frac{\int y d m}{\int d m}, z_{c m}=\frac{\int z d m}{\int d m}
$$

Where dm is mass of a small element. $x, y, z$ are the coordinates of the dm part.

Important points about the position of centre of mass

Its position is independent of the coordinate system chosen.
Its position depends upon the shape of the body and the distribution of mass.

And depending on this it may lie inside of the body as well as outside the body.

For symmetrical bodies having a homogenous distribution of mass, the centre of mass coincides with the geometrical centre of the body.
It changes its position only under the translatory motion whereas there is no effect on its position because of the rotatory motion of the body.

Centre of gravity-

Centre of gravity of a body is a point, through which the resultant of all the forces experienced by various particles of the body due to the attraction of the earth, passes irrespective of the orientation of the body.
If the body is located in a uniform gravitational field, then the centre of mass coincides with the centre of gravity of the body, and if not then its centre of mass and centre of gravity will be at two different locations.