Speed of Center of Mass – Rankers Physics
Topic: Center of Mass , Momentum and Collision
Subtopic: Motion of Center of Mass

Speed of Center of Mass

Two particles which are initially at rest, move towards each other under the action of their internal attraction. If their speeds are $v$ and $2v$ at any instant, then the speed of centre of mass of the system will be:

(2010 Pre)

$v$
$2 v$
Zero
$1.5 v$

Solution:

Concept: Since external force on the system is zero, the acceleration of the center of mass is zero. Formula: $v_{cm} = \frac{\sum m_i v_i}{\sum m_i}$. Solution: Since the system starts from rest and only internal forces act, velocity of center of mass remains zero.

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