Topic: The height s above the ground at time t of an object is given by s(t) = -5t2 + vot + so where s is in meters, t is in seconds, v0 is the object's initial velocity in meters per second and s0 is its initial position in meters. a) If you throw a ball straight up from the ground with an initial velocity of 20 meters per second, how long will it take for the ball to hit the ground? Explain your reasoning. b) If you now throw the ball from the top of a tower which is 80 meters above ground, at the same initial velocity as in part a), when does it hit the ground? Explain your reasoning.