# Homework Help: Conservation of Momentum and Kinetic Energy

1. Nov 19, 2008

### Blangett

1. The problem statement, all variables and given/known data

I was wondering if a glider hits a rubber band bumper is kinetic energy conserved? I can't tell if the data I have supports conservation or loss. I am writing a lab report and data shows that momentum had around a 5% change. Kinetic energy had a 10%-15% change. Momentum is always conserved in a collision so I can conclude its conservered in this case. What is worrying me is that my data is wrong because momentum had a 5% change, I am not sure at what percentage makes it not conserved. I think Kinetic energy is not conserved in this case. Am I right?

Mass ~ 0.1833

Velocity Before
v1=0.4109
v2=0.4327
v3=0.5959

Velocity After
v1= 0.3898
v2= 0.4083
v3= 0.5462

2. Relevant equations

K= 1/2*m*v2

p= m*v

Percentage of change 1 - (kinetic before/kinetic after)

percentage of change momentum 1 - (momentum before/momentum after)

3. The attempt at a solution

(.013925671/0.015474070) = .89999 so 90% is conservered a 10% change

(0.01527887/0.017159564) = .890 so 89% is conserved a 11% change

(0.027342351/0.032544623) = .840 so 86% is conserved a 14% change

It seemed that the larger the velocity the more kinetic energy is lost. I am worried my conclusion is completely inaccurate.

2. Nov 20, 2008

### Kurdt

Staff Emeritus
Do you think your situation is perfectly elastic?

3. Nov 21, 2008

### Blangett

I suppose its supposed to be since its a frictionless surface.