Option 2 : 500 kg

The correct answer is** 500 kg.**

__CONCEPT__:

- The type of collision in which there is a loss of kinetic energy and after the collision both the colliding particles move together is called perfectly inelastic collision.
- In this type of collision the coefficient of restitution is equal to 0.
- Momentum of the system remains constant in this collision.

- Momentum before collision (P1) = Momentum after the collision (P2)

P1 = m1u1 + m2u2

P2 = m1v1 + m2v2

__ CALCULATION__:

Here, speed of the car is 0 m/s

⇒ After collision speed is 8 m/s

According to "**Principle of conservation of momentum**"

⇒ So, 8 = (m_{1}v_{1} + m_{2}v_{2})/(m_{1} + m_{2}) where m_{1 }is the mass of truck, v_{1} is the velocity of truck, v_{2} is the velocity of car and m_{2} is the mass of car.

⇒ 8 = (2000 × 10 + m_{2} × 0)/(2000 + m_{2})

⇒ 16000 + 8 m_{2} = 20000