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

Question

You use and solve for V:
M1V1+M2V2=(M1+M2)V

I end up with the following because my question does not give the mass of the cars, it only states that they are identical, therefore M1=M2. I get:
90km/h=M1*V

What am i doing wrong?

Answer 1

You are not thinking. If M2=M1, then

V1+V2=2V
v= 45km/hr