what about a 5,000 kg truck rear-ends a 1200 kg car that has been traveling at 13 m/s, causing the truck to slow down from 14 m/s to 12 m/s and the car to speed up. What is the final velocity?

Answer 1

again, this should not be an elastic collision,
momentum change...
5000*(14-12)+1200(13+v)=0
(ie, the net change of momentum is zero.)

Solve for v, the final velocity of the car.

Answer 2

when I solve for that, i got -8.5 which can't be possible seeing the car started at 13.

did i do something wrong?

Answer 3

Arrrggggg.
change momentum = mass(vf-vi)!!!!
5000(12-14)+1200(V-13)=0

V-13=10000/1200
V=13+8.5=21.5m/s

Answer 4

got it! thank you so much!!