Posted by Elizabeth on .
A railroad car with a mass of 1.93 104 kg moving at 3.24 m/s joins with two railroad cars already joined together, each with the same mass as the single car and initially moving in the same direction at 1.16 m/s.
(a) What is the speed of the three joined cars after the collision?
1 m/s
(b) What is the decrease in kinetic energy during the collision?

Physics 
drwls,
(a) Assume and apply conservation of momentum.
1 m/s is not the answer.
(b) The initial total KE is (1/2)*1.93*10^4*(3.24)^2 J
+2*(1/2)*1.93*10^4*(1.16)^2 J
Subtract the final KE from that