1) What is the initial momentum of the first train car? 2) What is the mass of t

Question

1) What is the initial momentum of the first train car?

2) What is the mass of the second train car?

3)What is the change in kinetic energy of the two train system during the collision?

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 = 8.1 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.)

5)Compare the magnitude of the momentum of train car 1 before and after the collision:

a) p1 initial = p1 final

b) p1 initial > p1 final

c) p1 initial < p1 final

Explanation / Answer

m1 = 630 kg , v1 = 8.1 m/s , vf = 5 m/s

1 )

initial momentum = m1 v1 = 630 X 8.1 = 5130 kg.m/s

2 )

630 X 8.1 = ( 630 + m2 ) X 5

5130 = 3150 + 5 m2  

m2 = 1980 / 5

m2 = 396 kg

3 )

initial KEi = 1/2 X m1 v12  

KEi = 0.5 X 630 X 8.12

KEi = 20667.15 J

final KEf = 0.5 X ( m1 + m2 ) vf2

KEf = 0.5 X ( 630 + 396 ) X 52  

KEf = 12825 J

change in KE = KEf - KEi = 12825 - 20667.15

KE = - 7842.15 J

4 )

630 X 8.1 - 396 X 6 = 1026 X vf

5103 - 2376 = 1026 vf

vf = 2.65 m/s

5 )

option : b is correct

P1 initial > P1final

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