Consider a system to be one train car moving toward another train car at rest. when the train cars collide, the two cars stick together. what is the total momentum of the system after the collision? 800 kg • m/s 1,600 kg • m/s 2,400 kg • m/s 4,000 kg • m/s

Monarch butterflies have brightly colored orange wings with black patterns on them, making them easily visible to birds that eat butterflies and moths, yet birds rarely eat the monarchs. likewise, the monarch caterpillars are brightly striped yellow and white and black, and they also are rarely eaten by birds, although some wasps will attack them and feed them to their young. what can be inferred from these observations? monarchs must threaten and attack birds, but not wasps. monarchs have a way of discouraging bird predation that does not involve hiding. monarchs’ wings are so colorful that most birds must find them difficult to eat. monarchs lay more eggs than other less conspicuous butterflies.