F4. A model rocket initially at rest at ground level is launched upward starting at time / = 0. The rocket has an upward acceleration as long as its engine is firing, but once the engine stops firing, the rocket is in free-fall until is reaches the ground again. The rocket's motion is purely vertical. The graph to the right shows the velocity of the rocket as a function of time, where positive values represent upward velocity. The graph is NOT to scale, which means that the times 7, 72, and 7, marked on the horizontal axis are NOT necessarily equally spaced apart. (a) Explain what the rocket is doing at time / = 7, seconds. (b) i. Which is greater: the greatest upward speed reached by the rocket, or the greatest downward speed? Greatest upward speed Greatest downward speed Both are equal Which is greater: the time the rocket spends moving upward, or the time spent moving downward? Time moving upward Time moving downward Both are equal iii. Explain your previous two answers in a well-reasoned, organized paragraph. Cite appropriate physical principles and use the graph shown above or construct one of your own