Growth Speed The images of trees in Figure P1.68 come from a catalog advertising fast-growing trees. If we mark the position of the top of the tree in the successive years, as shown in the graph in the figure, we obtain a motion diagram much like ones we have seen for other kinds of motion. The motion isn’t steady, of course. In some months the tree grows rapidly; in other months, quite slowly. We can see, though, that the average speed of growth is fairly constant for the first few years. What is the tree’s speed of grow?th, in feet ?per year, from ?t = 1 yr t? = 3 yr? A. 12 ft/yr B. 9 ft/yr C. 6 ft/yr D. 3 ft/yr

ANSWER: Here the growth of the tree is given in units of feets for each year. In the 1 st yr (1 to 2 nd yr) the height of the tree increased by, 21 - 12 = 9 feet. In the 2 nd yr (2 to 3rd yr) the height increased by 30 - 21 =9 feet. The total growth of the...