Assume that the boxcars all have the same mass.
Use conservation of momentum:
2*m*vi = 3*m*vf
where m is the mass of one boxcar, vi is the initial speed, vf is the final speed.
2*m*4 = 3*m*vf
vf = 8/3
Initial kinetic energy is ki
1/2*(2*m)*vi^2 = m*4^2 = 16*m
Final kinetic energy kf is
1/2*(3*m)*(8/3)^2 = 1/2*(3*m)*(64/9) = (32/3)*m
The fraction of the car's initial kinetic energy that is transformed into thermal energy is (ki - kf)/ki
Two coupled boxcars are rolling along at 4.0 when they collide with and couple to a third, stationary boxcar.
1.) What is the final speed of the three coupled boxcars?
2.) What fraction of the cars' initial kinetic energy is transformed into thermal energy?
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