A train car with mass m 1 = 678 kg is moving to the right with a speed of v 1 =

Question

A train car with mass m1 = 678 kg is moving to the right with a speed of v1 = 7.7 m/s and collides with a second train car with mass m2 = 761 kg. The two cars latch together during the collision.

1)

What is the magnitude of initial momentum of BOTH train cars?

kg-m/s

2)

What is the final speed of the train cars latched together?

m/s

3)

What is the change in total momentum of the two train system during the collision?

kg-m/s

4)

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 = 7.7 m/s and collides with the second train car that is now moving to the left with a speed of v2 = 8.5 m/s before the collision. The first car rebounds backwards (to the left) at a speed of v3 = 4.5 m/s.

What is the final velocity of the second car? (A positive velocity means the train car moves to the right – a negative velocity means the train car moves to the left.)

m/s

5)

Compare the total kinetic energy of the SYSTEM before and after the collision:

KEinitial = KEfinal

KEinitial > KEfinal

KEinitial < KEfinal

Explanation / Answer

1)initial momentum of m1=678*7.7=5220.6 kg-m/s

initial momentum of m2=0

2) let final speed be v

5220.6=(678+761)v

v=3.63 m/s

3)the momentum is conserved. Therefore, the momentum does not change

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