Question

Benjamin threw a rock straight up from a cliff that was 60 ft above the water. If the height of the rock​ h, in​ feet, after t seconds is given by the equation ​h=-16t^2+68t+60, how long will it take for the rock to hit the​ water?

Answer 1

5 sec

Explanation:

Hit the water, means h = 0

Solve -16t^2 + 68t +60 =0

4t^2 - 17t - 15 = 0

(4t + 3)(t - 5) = 0

so t = 5 sec