Answer:
v=9.6 km/s
Step-by-step explanation:
Given that
The mass of the car = m
The mass of the truck = 4 m
The velocity of the truck ,u= 12 km/s
The final velocity when they stick = v
If there is no any external force on the system then the total linear momentum of the system will be conserve.
Pi = Pf
m x 0 + 4 m x 12 = (m + 4 m) x v
0 + 48 m = 5 m v
5 v = 48
![v=(48)/(5)\ km/s](https://img.qammunity.org/2021/formulas/physics/college/d9qq53hf5noyl68ewtbott4khojeslzd6g.png)
v=9.6 km/s
Therefore the final velocity will be 9.6 km/s.