To determine the momentum of an object, we use the formula for momentum:
[tex]\[
\text{momentum} = \text{mass} \times \text{velocity}
\][/tex]
In this problem, we are given:
- The mass of the tire ([tex]\(m\)[/tex]) is [tex]\(15 \, \text{kg}\)[/tex].
- The velocity of the tire ([tex]\(v\)[/tex]) is [tex]\(3 \, \text{m/s}\)[/tex].
Using the formula for momentum, we can substitute the given values:
[tex]\[
\text{momentum} = 15 \, \text{kg} \times 3 \, \text{m/s}
\][/tex]
Multiplying these values together:
[tex]\[
\text{momentum} = 45 \, \text{kg} \cdot \text{m/s}
\][/tex]
Therefore, the momentum of the 15 kg tire rolling down the hill at [tex]\(3 \, \text{m/s}\)[/tex] is:
[tex]\[
\boxed{45 \, \text{kg} \cdot \text{m/s}}
\][/tex]