The boy jumps off the flat car at A with a velocity of = 4 ft/s relative to the car as...

The boy jumps off the flat car at A with a velocity of = 4 ft/s relative to the car as shown. If he lands on the second flat car B, determine the final speed of both cars after the motion. Each car has a weight of 80 lb. The boy's weight is 60 lb. Both cars are originally at rest. Neglect the mass of the car's wheels.