Answer:
1.5 seconds
Step-by-step explanation:
h=-16t² – 16t+ 60
When the rock enter the water, the height is 0. ... h=0
0 = -16t² – 16t+ 60 = -4 * (4t² - 4t +15) = -4* (2t - 3) (2t +5)
2t-3=0 or 2t+5 = 0
t = 3/2 or t = -5/2 (time can't be negative)
t = 3/2 or 1.5
