From a height of 20 meters, a stone is thrown downwards at 15 m/s. What is the velocity just as it hits the ground?

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.