A railroad car of mass 2.7 10^4 kg moving at 4.50 m/s collides and couples with

Question

A railroad car of mass 2.7 10^4 kg moving at 4.50 m/s collides and couples with two coupled railroad cars, each of the same mass as the single car and moving in the same direction at 1.20 m/s. (a) What is the speed of the three coupled cars after the collision? Your response differs from the correct answer by more than 10%. Double check your calculations. m/s (b) How much kinetic energy is lost in the collision? Your response differs from the correct answer by more than 10%. Double check your calculations. J

Explanation / Answer

from the conservation of momentum

m1u1+m2u2=m1v1+m2v2

2.7*10^4(4.5+1.2)=(m1+m2)*v

v=2.85 m/sec

initial kinetic energy=1/2m1u1^2+1/2m2u2^2

ki=1/2*2.7*10^4(4.5^2+1.2^2)=29.28*10^4 J

finala kinetic energy kf=1/2(m1+m2)*v^2

kf=2.7*10^4*2.85^2=21.93*10^4 J

loss in kinetic energy=(ki-kf)/ki*100=25.1%

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