Hi, i really need help with this question.

Two identical cars hit each other and lock bumpers. A car moving with a speed of 90 km/h approaches a stationary car

and what is the question?

You cannot use conservation of energy here, only conservation of momentum.

The question is: two identical cars hit each other and lock bumpers. If a car moving with a speed of 90km/h appraoches a stationary car, what is the speed immediately after coupling cars.

M1V1+M2V2=(M1+M2)V

solve for V

Thank you that was bothering me for so long.

In the problem, the mass isn't known though, you know that the one car is identical to the other though. i end up getting,

90km/h=M1*V

What do I do after that?

Sure, I'd be happy to help you with that question. Could you please provide me with the complete question or the information you have?