# Momentum Multiple choice question

A billiard ball has an initial speed of 5 m/s and it collides with another billiard ball of the same mass initially at rest. If the speeds of the two billiard balls are 3 and 4 m/s, then

a) momentum was conserved but not kinetic energy
b) kinetic energy was conserved but not momentum
c) momentum and kinetic energy were both conserved
d) neither momentum or kinetic energy were conserved

I saw that KE initial=KE final by doing:

(1/2)(m)(5)^2 = (1/2)(m)(3)^2 + (1/2)(m)(2)^2

I thought momentum was not conserved since P initial does not equal P final:
5m not equal to 4m +3m... so I thought the answer was B

The answer is C though...thanks for any help in advance.

## Answers and Replies

A billiard ball has an initial speed of 5 m/s and it collides with another billiard ball of the same mass initially at rest. If the speeds of the two billiard balls are 3 and 4 m/s, then

a) momentum was conserved but not kinetic energy
b) kinetic energy was conserved but not momentum
c) momentum and kinetic energy were both conserved
d) neither momentum or kinetic energy were conserved

I saw that KE initial=KE final by doing:

(1/2)(m)(5)^2 = (1/2)(m)(3)^2 + (1/2)(m)(2)^2

hope that helps :]