# A ball with a mass of #2 kg# is rolling at #9 m/s# and elastically collides with a resting ball with a mass of #1 kg#. What are the post-collision velocities of the balls?

##### 2 Answers

No

No

the speed after collision of the two objects are see below fro explanation:

#### Explanation:

Because there are two unknown I am not sure how you able to solve the above without using, conservation of momentum and conservation of energy (elastic collision). The combination of the two yields 2 equation and 2 unknown which you then solve:

Conservation of "Momentum":

Let,

Conservation of energy (elastic collision):

We have 2 equations and 2 unknowns:

From (1) ==>

From (2) ==>

Insert

Using the quadratic formula:

The solution that make sense is 2.64 (explain why?)

Insert in (3) and solve

So the speed after collision of the two objects are:

#### Explanation: