The velocity of the 2x10^4 kg car just before the collision is 0 m/s.
When two bodies of different masses move together each other and have head on collision, they travel to same or different direction after collision.
The external force is not acting here, so the initial momentum is equal to the final momentum. For inelastic collision, final velocity is the common velocity for both the bodies.
m₁u₁ +m₂u₂ =(m₁ +m₂) v
Substitute the values for m₁ = 1.5 x 10^4 kg, m₂ =2 x 10^4 kg and u₁ =7 m/s, the final velocity is 3m/s/
1.5 x 10^4 x 7+2 x 10^4 x u₂ = (1.5 x 10^4 + 2 x 10^4) x 3
u₂ = 0 m/s
So, the car with mass 2x10^4 kg is stationary.
Thus, the velocity of the 2x10^4 kg car just before the collision is 0 m/s.
Learn more about conservation of momentum principle
https://brainly.com/question/14033058
#SPJ1