4. A train car with mass m1 = 684 kg is moving to the right with a speed of v1 = 7.2 m/s and collides with a second train car. The two cars latch together during the collision and then move off to the right at vf = 4.4 m/s.

Question

b) Now the same two cars are involved in a second collision. The first car is again moving to the right with a speed of v1 = 7.2 m/s and collides with the second train car that is now moving to the left with a velocity v2 = -5.4 m/s before the collision. The two cars latch together at impact.

What is the final velocity of the two-car system? (A positive velocity means the two train cars move to the right – a negative velocity means the two train cars move to the left.)

please explain with the answer

Answer 1

conservation of momentum applies
intital momentum = final
m1*V1+M2*V2= (M1+M2)Vf
put in the numbers (V2 to the left means -), solve for Vf