# Conservation of Linear Momentum Problem (Need help)

1. Mar 25, 2015

### Kaleem

1. The problem statement, all variables and given/known data
A 4.60-kg ball, moving to the right at a velocity of +2.31 m/s on a frictionless table, collides head-on with a stationary 9.80-kg ball. Find the final velocities of (a) the 4.60-kg ball and of (b) the 9.80-kg ball if the collision is elastic. (c) Find the magnitude and direction of the final velocity of the two balls if the collision is completely inelastic.
2. Relevant equations
P = (mvf1+mvf2) - (mvi1+mvi2)

3. The attempt at a solution
I understand part c since they will have a combined mass and the same final velocity and that Vi2=0 however i can't figure out how to solve parts A and B.

2. Mar 25, 2015

### BruceW

hi, welcome to physicsforums :)
For part a) and b) you are meant to assume the collision is elastic. So what kind of condition is this? and can you use this to find an answer to the problem?

3. Mar 25, 2015

### Kaleem

Since the collision is elastic would it be safe to assume that kinetic energy is conserved?

4. Mar 25, 2015

### BruceW

yes! and what else is conserved in the collision?

5. Mar 25, 2015

### Kaleem

I'm not exactly sure, is it mechanical energy?

6. Mar 26, 2015

### BruceW

there are not potential energies here. Think of something else that is conserved in collision. (hint: it is conserved in inelastic collisions too).

7. Mar 26, 2015

### Satvik Pandey

As there is a elastic collision so you can use that ($e$(coefficient of restitution)=1). So velocity of separation is equal to the velocity of approach in common normal direction. This will give you a relation between the velocities of the balls. You have mentioned a name of a concept in the title of this thread. Just use that concept.