Solving Rotational Problem: Conserving Momentum, Energy & Mass

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Homework Help Overview

The discussion revolves around a physics problem involving a stick and a ball, focusing on the conservation of momentum, energy, and mass during an elastic collision. The problem specifically asks which quantities are conserved and what conditions must be met for the ball to remain at rest after the collision.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the conservation of linear momentum, angular momentum, and kinetic energy, questioning how these principles apply to the scenario. There is uncertainty about the correct approach to take given the elastic nature of the collision.

Discussion Status

Some participants have provided clarifications regarding the conservation laws applicable in collisions without external forces. There is an ongoing exploration of the implications of the term "elastically" and its significance in the context of the problem.

Contextual Notes

Participants are discussing the definitions and implications of elastic collisions, particularly the conservation of kinetic energy and the coefficient of restitution. There is an acknowledgment of potential confusion regarding the application of different conservation principles in this specific scenario.

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Homework Statement


A stick of length L and mass M lies on a frictionless horizontal surface on which it is free to move in anyway.
A ball of mass m moving with speed v collides elastically with the stick at a distance d below its centre.
(a) Which quantities are conserved in this collision?
(b) What must be the mass of the ball so that it remains at rest immediately after collision?



Homework Equations





The Attempt at a Solution


Here if we conserve linear momentum,
we get mv=Mv1 (As the ball remains at rest.)
But I don't think this is right because if we conserve angular momentum, then we get something else, and if we conserve kinetic energy, then we get something else.
So fow do i go about this question?
 
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Hi iitjee10! :smile:

i] in any collision (with no external forces), both momentum and angular momentum are always conserved

ii] what does "elastically" mean?
 
ii] what does "elastically" mean?
It means they collide with no loss of kinetic energy. :wink:
 
elastically means coefficient of restitution is 1
 

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