An empty train car moving at 21 m/s collides with a loaded train car initially at rest that has twice the mass of the empty car. The two cars couple together. a) What is the final velocity of the cars after the collision? 7 m/s
b) Is kinetic energy conserved in this collision? If so, how do you know? If not, why is there a difference?

16. a brave but inadequate rugby player is being pushed backward by an opposing player who is exerting a force of 800 n on him. the mass of the losing player plus equipment is 90.0 kg, and he is accelerating at 1.20m/s2 size 12{1 "." "20"" m/s" rsup { size 8{2} } } {} backward. (a) what is the force of friction between the losing player’s feet and the grass? (b) what force does the winning player exert on the ground to move forward if his mass plus equipment is 110 kg? (c) draw a sketch of the situation showing the system of interest used to solve each part. for this situation, draw a free-body diagram and write the net force equation.