# Physics

A rock dropped from a bridge takes 3.21 seconds to hit the water. How high is the bridge in meters?

I need to find Vsub0 to be able to calculate h....but how do I get Vsub0???

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1. is it -9.80 x 3.21= -31.458 is Vsub0??

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2. h=151.47m??

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3. the initial speed is zero. It was dropped, not thrown.

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4. accck ok so

1/2(9.80)(3.21)^2= 50.5 m

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5. (1/2)(9.81)(3.21)^2 = 50.5 meters

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6. I'm learning slowly but surely!

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7. more formally
h = Hi + Vi t - 4.9 t^2
0 = Hi + 0 - 4.9 t^2
Hi = 4.9 *3.21^2 = 50.5

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8. yes, good

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