Asked by Marcus

Ben throws a ball vertically upward from the top of a cliff. The height of the ball above the base is approximated by the model h = -5t² - 5t + 100, where h is the height in metres and t is the time in seconds.
a) After how many seconds does the ball hit the ground?
b) How long does it take for the ball to reach a height of 40 metres above the base of the cliff?
Answered by Reiny
a) set -5t² - 5t + 100 = 0 and solve for t
hint: divided all terms by -5, and then it factors nicely

b) -5t² - 5t + 100 = 40
solve as a quadratic using your favourite method