試題詳解

5. Suppose a person standing at the top of a building 240 feet high throws a ball vertically upward with an initial velocity of 32 A/sec. When is the velocity 0? What is the significance of this time? Hint: Suppose the height of the ball above the ground at time t is H(t) = -16t²+ b t+c feet.
(A) The ball is at its lowest point when t = 3 second.
(B) The ball is at its lowest point when t = 2 second.
(C) The ball is at its highest point when t = 1 second.
(D) The ball is at its highest point when t= 5 second.