Question

A train car with mass m1 = 515 kg is moving to the right with a speed of v1 = 7.5 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 = 4.8 m/s.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 = 7.5 m/s and collides with the second train car that is now moving to the left with a velocity v2 = -6 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.)

Answer 1

For the first situation, we first need to find the mass of the second train car.

In order to do that, we apply the conservation of the amount of movement:

`515*7.5+m2*0=(m1+m2)*4.8`

and we have as a result:

m2 = 289.6875

For the second situation, also we will apply the conservation of the amount of movement:

`515*7.5-289.6875*6 = (515+289.6875)*V`

and we have as a result:

V = 2.64 (it is moving to the right)