How Do You Determine the Mass of the Second Object in an Elastic Collision?

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Homework Help Overview

The discussion revolves around determining the mass of a second object involved in an elastic collision with a first object of known mass. The first object has a mass of 3.6 kg and is moving in the positive x direction, while the second object's final speed is stated to be eight times that of the first object after the collision.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the conservation of momentum and energy equations relevant to elastic collisions. There are questions about the initial conditions of the second object and the implications of its mass in relation to the first object. Some participants suggest using the coefficient of restitution as a potentially simpler approach.

Discussion Status

The discussion is ongoing, with participants exploring different methods to approach the problem. Some have raised questions about the initial state of the second object and the conservation laws applicable to the scenario. There is no explicit consensus on the best approach yet.

Contextual Notes

There is uncertainty regarding whether the second object is at rest before the collision, which affects the conservation laws being applied. Participants are also considering the implications of the mass of the second object in relation to the final speeds post-collision.

katrvu
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An object with mass 3.6 kg is moving in the positive x direction when it strikea second object head-on. THe collision is elastic and afterwards both objects are moving in the positive x direction. If the final speed of the second object is equal to 8 times the final speed of the first object, what is the mass of the second object?

answer should be 2.62 kg. anyone knows how to solve it?

Thank you so much
 
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how did you try to approach the problem?
 
well, it says it's elastic collision. so I came up with the following conservations:
let x direction be positive
1. from conservation of momentum
mv1-mv2=mv1f+mv2f
mv1-mv2=mv1f+m8v1f

2. from conservation of energy
1/2mv1^2+1/2mv2^2=1/2mv1f^2+1/2mv2f^2
mv1^2+mv2^2=mv1f^2+m64v1f^2

but there are so many unknows.. donno where to go from here
 
It would be wiser to use the co-effecient of restitution here. The energy equation gets tedious. ;)
 
Is the second object at rest when it is struck by the first object? What quantity has to be conserved in the described collision? What additional quantity is conserved if the collision is elastic (no energy dissipation)?

Next, let's do a thought experiment: Suppose the mass of the second object were the same as the first, what would the results of the collision be? Based on this result, and the description of of the unknown collision, is the mass of the second object more or less than the first?
 
Bob S said:
Is the second object at rest when it is struck by the first object? What quantity has to be conserved in the described collision? What additional quantity is conserved if the collision is elastic (no energy dissipation)?

Next, let's do a thought experiment: Suppose the mass of the second object were the same as the first, what would the results of the collision be? Based on this result, and the description of of the unknown collision, is the mass of the second object more or less than the first?

based on the question the 2nd object must be less because it's final speed is much faster, this is because of impulse I believe. The question doesn't say 2nd object is at rest, so 2nd object should have initial speed and collide head on. any suggestions?
thanks
 
any idea?
 

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