Given data:
* The mass of the truck is m_1 = 3000 kg.
* The mass of the parked car is m_2 = 1000 kg.
* The initial velocity of the truck is u_1 = 10 m/s.
* The initial velocity of the parked car is u_2 = 0 m/s.
* The final velocity of the car is v_2 = 15 m/s.
Solution:
According to the law of conservation of momentum, the net momentum of the system before and after the collision is the same.
Thus,
![m_1u_1+m_2u_2=m_1v_1+m_2v_2](https://img.qammunity.org/2023/formulas/physics/college/t4onuxsn89xbdlh5ekaiaqhm93negpbhfl.png)
Substituting the known values,
![\begin{gathered} 3000*10+1000*0=3000v_1+1000*15 \\ 30000+0=3000v_1+15000 \\ 3000v_1=30000-15000 \\ 3000v_1=15000 \end{gathered}](https://img.qammunity.org/2023/formulas/physics/college/hytcncna1zm5xgzzkb1q2sfv57ignvg5np.png)
By simplifying,
![\begin{gathered} v_1=(15000)/(3000) \\ v_1=5\text{ m/s} \end{gathered}](https://img.qammunity.org/2023/formulas/physics/college/cbluwgvpbibqfvvjyh403jh27myd8geg18.png)
Thus, the velocity of the truck is 5 meters per second.