Find the coefficient of restitution between the balls (should be easy)

[daletron]

Homework Statement

i'm retaking a test question for half credit and this is the 3rd part to the question. i know the velocities are correct because the teacher gave us the answers.

this SHOULD be simple... but okay.. (velocity) V1 = 20ft/s, V2 = 0ft/s. after the collision V1` = 16ft/s, V2` = 4ft/s. I'm supposed to find the coefficient of restitution. The formula for that (Partially elastic i assume) is (V1` - V2`) = -e(V1-V2). I get -.6 for e. but isn't e supposed to be between 0 and 1? the e is SUPPOSED to be 1/3 (given by the teacher). and I'm pretty sure i didn't copy that down wrong so it just doesn't make sense to me

Homework Equations

(V1` - V2`) = -e(V1-V2)

The Attempt at a Solution

(16ft/s - 4ft/s) / -20ft/s = -.6

Picture of the problem
http://i11.photobucket.com/albums/a162/daletron/untitled.jpg

 

[andrevdh]

First use momentum conservation to determine the speeds of the balls along the given directions.

 

[daletron]

First use momentum conservation to determine the speeds of the balls along the given directions.

i did, hence when i said "after the collision V1` = 16ft/s, V2` = 4ft/s"

 

[andrevdh]

For the restitution you need to consider the speeds of the objects along the line of action. Collisions without friction changes the velocity components of the objects along the line of action. The components perpendicular to these are unaffected by the collision.