# A ball with a mass of #2 kg# is rolling at #7 m/s# and elastically collides with a resting ball with a mass of #4 kg#. What are the post-collision velocities of the balls?

##### 1 Answer

Jan 27, 2017

v1 = -2,33 m/s

v2 = 4,66 m/s

#### Explanation:

in the elastic collisions remain constant both the total kinetic energy both the momentum. Therefore:

replacing the values in the equation of conservation of momentum, you find:

(1)

that you put in the equation of conservation of energy.

Resolving the second degree equation, you find:

then

If You put in the (1), you find:

If you put the values in the equation of conservation of energy, you find that it is verified