Final answer:
The velocity of the semi-truck is 1.5m/s.
Step-by-step explanation:
To find the velocity of the semi-truck, we can use the formula:
Momentum (p) = mass (m) * velocity (v)
Given that the mass of the semi-truck is 1200kg and the momentum is 1800kg·m/s, we can rearrange the formula to solve for velocity:
Velocity = Momentum / Mass = 1800kg·m/s / 1200kg = 1.5m/s
Therefore, the velocity of the semi-truck is 1.5m/s.