Please help me!!I dont understand?

Question

A rock is dropped from the top of a 15 m tall building. How fast is it moving just before it strikes the ground? (Notice that you don't need to know the mass to solve this problem because it cancels out of the equation.) .

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the anawer is 17.3....how did they get this?

Answer 1

Final Velocity = Sqr ( Initial Speed ^2 + H * g * 2 )

Initial Velocity = 0, so lets use H * g * 2

Final Velocity = Sqr ( 15 * 10 * 2 )

Final Velocity = Sqr (300) = 17.32m/s

Answer 2

V^2 = Vo^2 + 2 * g * H

V^2 = 0 + 2 * 9.8 * 15

V^2 = 294

V = 17.1 m/s

Good Luck!