SOLUTION: Benjamin threw a rock straight up from a cliff that was 100 ft above the water. If the height of the rock h, in feet, after t seconds is given by the equation h=-16t^2 +60t +100 ho
Algebra ->
Customizable Word Problem Solvers
-> Evaluation
-> SOLUTION: Benjamin threw a rock straight up from a cliff that was 100 ft above the water. If the height of the rock h, in feet, after t seconds is given by the equation h=-16t^2 +60t +100 ho
Log On
Question 946130: Benjamin threw a rock straight up from a cliff that was 100 ft above the water. If the height of the rock h, in feet, after t seconds is given by the equation h=-16t^2 +60t +100 how long will it take for the rock to hit the water? Answer by Edwin McCravy(20056) (Show Source):
·h = 126 ft. highest point rock reaches before it starts to fall
| [you don't need to know it is 126 ft. (vertex formula)]
cliff |
---------·h = 100 ft (cliff level)
|
|
|
|
---------·h = 0 ft. (water level)
Since the water level is 0, we set h=9 and solve for t:
h = -16t² + 60t + 100
0 = -16t² + 60t + 100
divide both sides by -4
0 = 4t² - 15t - 25
0 = (2t+5)(t-5)
0 = 2t+5; 0 = t-5
-5 = 2t; 5 = t
-5/2 = t;
Ignore the negative answer.
Answer: 5 seconds.
Edwin
