1. Oct 21, 2007

### arpitm08

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

Two balls of equal mass moving with the speed of 3 m/s, collide head on. Find the speed of each after impact if the coefficient of restitution is 1/3.

2. Relevant equations

e=(v2-v1)/(u1-u2)
v2= velocity after impact of object 2
v1= velocity after impact of object 1
u2= velocity before impact of object 2
u1= velocity before impact of object 1

3. The attempt at a solution

I put the numbers into the equation and it yield 0 over something.
The answer is 1 m/s for both ball, but with that into the equation, it would yield 0/0.
My book doesn't say anything on how to do this problem. Maybe it is as simple as multiplying the velocities by 1/3 to get the answer.

Last edited: Oct 21, 2007
2. Oct 21, 2007

### Staff: Mentor

direction counts!

Since the balls approach each other, one has a velocity of +3 m/s while the other has a velocity of -3 m/s.

3. Oct 21, 2007

### arpitm08

yes that is true, but i just copied the problem exactly from the book.

4. Oct 21, 2007

### Staff: Mentor

There's nothing wrong with the problem statement, just with your attempted solution.
That just means you input the wrong numbers. Realize that u and v are velocities, not just speeds.

5. Aug 8, 2008

### ajinx999

Considering
u1 = 3 m/s
u2 = -3 m/s
e = 1/3
e = (v2-v1)/(u1-u2)
→ v2-v1 = 2 m/s
u1+u2=v1+v2
...(conservation of linear momentum)
→ v1+v2 = 0
→ v1 = -v2
Therefore, the speed of each ball after impact is 1 m/s.