# Homework Help: How do I calculate percent elasticity?

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1. Mar 29, 2015

### xxyourstruly

1. The problem statement, all variables and given/known data
I was given a chart to figure out the different momentum and kinetic energies of different collisions (elastic and inelastic) and in the lab he posed the question "Calculate the percent elasticity for each of the collisions."

2. Relevant equations
conservation of momentum and energy

3. The attempt at a solution
I have never heard of this question before and have looked through all of my notes. Finding nothing, I turned to the internet and searched for "percent elasticity," "how to calculate percent elasticity," and multiple other relevant phrases to the problem. Nothing has come up so far and I'm not sure how to approach the question. Any help would be awesome. Thanks!

2. Mar 29, 2015

### AlephNumbers

How are elastic collisions different from inelastic collisions?

3. Mar 30, 2015

### xxyourstruly

Elastic collisions occur when objects of whatever mass or velocity collide and propel apart from each other with the exact same momentum and energy as the initial momentum and energy (p=p' and E=E'). Inelastic collisions are when objects of whatever mass or velocity collide and 'stick' together. For example, two tennis balls with Velcro stick together when they collide. In this system, energy is lost.

4. Mar 30, 2015

### AlephNumbers

Right! Energy is not conserved in inelastic collisions. Think of a collision in which energy is conserved. This case could be described as being 100% elastic, right? Alternatively, think of a case in which the collision is completely inelastic. This case could be described as being 0% elastic. The final kinetic energy of the system is not zero, but the elasticity is still 0%.

5. Mar 30, 2015

### AlephNumbers

Well, actually, the kinetic energy is not conserved. Energy is always conserved. Some of it just goes into heat or sound or what have you.

6. Mar 30, 2015

### xxyourstruly

Okay, yeah that makes sense! Thank you so much!