SOLUTION: If a rock is dropped off of a bridge that is 30 feet above a river, how long will it take to hit the water?

Question 287134: If a rock is dropped off of a bridge that is 30 feet above a river, how long will it take to hit the water?
Found 2 solutions by nyc_function, qiuli:
Answer by nyc_function(2741) (Show Source): You can put this solution on YOUR website!
I need more information. I need to know how fast the rock is falling.
Then I can make an equation. Understand? There is a typo here.
Answer by qiuli(1) (Show Source): You can put this solution on YOUR website!
You can use the vertical motion model for this problem: f(x)=-16x^2+vx+s, f(x) being height, v being initial velocity and s being the starting height.
As there is no starting height, the problem can be stated as -16x^2+30.

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