Answer:
Time(s) the ball is lower than the bridge is (2, 3.385)
Here (-∞,0) is not included because time cannot be negative, it is always positive.
Explanation:
We have equation rock given by -16t²+32t+75.
At t = 0 the height is 75 m.
We need to find after how much time the height is less than 75.
That is
-16t²+32t+75 ≤ 75
-16t²+32t ≤ 0
16t² - 32 t ≥ 0
t² - 2t ≥ 0
t (t-2) ≥ 0
That is t ≥ 2
We also need to check when the stone reaches ground, that is
-16t²+32t+75 = 0
On solving we will get
t = 3.385 s and t = -1.385 seconds ( not possible)
So at time 3.385 seconds stone reaches ground.
So, Time(s) the ball is lower than the bridge is (2, 3.385)
Here (-∞,0) is not included because time cannot be negative, it is always positive.