# B Coefficient of Restitution in x and y

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1. May 28, 2017

### unseeingdog

I am currently studying collisions in high school and my teacher told us that, in order to calculate the direction of each object after a 2-body collision, we could change the values in the relative velocity terms of the equation of the coefficient of restitution to the components in x and y. Is this true? Thanks.

2. May 29, 2017

### Ssnow

If collisions are on a line, you can fix a positive orientation of the line so you have positive and negative velocities respect the two opposit directions... it is possible to interpret the minus in front of the vector as a velocity in the opposite sense ...
If the collision is in the plane you can always do the same component by component ....
I don't know if I answered ...
Ssnow

3. May 29, 2017

### unseeingdog

So, say, if one of the bodies moves along the x axis, and the other moves with an angle of 120 with respect to the horizontal, one can write $e_x = (v_2cos(120) - v_1)/(u_1 - u_2cos(120)$ ?

4. May 29, 2017

### Ssnow

mmmmh, what is $e_{x}$ ? ...... if the $\vec{v}=(v_{1},v_{2})$ is the first vector and $\vec{u}=(u_{1},u_{2})$ the second forming an angle of $120°$ then $\vec{v}=(v_{1},0)$ because is on the $x$ axis and $\vec{u}=(u\cos{(120)},u\sin{(120)})$ where $u$ is the magnitude of $\vec{u}$. Now you must fix a sign $\pm$ to each component that describes the collision ...
Ssnow

5. May 29, 2017

### unseeingdog

I meant $e_x$ to be the coefficient of restitution. Sorry for not specifying. Anyways, I get it now. Thanks