A boy standing on a bridge throws a ball up at the speed of 20m/s, the ball aftr 3 seconds touches water surface below. Can you calculate the height of bridge to be 5m?


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Oddman answered
Unless the boy is on another planet, the problem as stated makes no sense. With Earth's gravity (a=-9.8m/s^2) being the only influence on the ball, at the end of 3 seconds it will be
  h = v0t - (1/2)at2 = 20(3) - (1/2)(9.8)(3^2) = 15.9
meters above where it was thrown from.

The surface of the water in the aqueduct is 15.9 m above the point of release of the ball. There is not enough information to tell the height of the bridge.

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