How long (in seconds) does it take the stone to hit the water?

Question

A stone is thrown downward with an initial velocity of 2.8 m/sm/s from a bridge which is H� = 48 mm above water. The magnitude of the gravitational acceleration is 9.8m/s². Take DOWNWARD as positive direction.

Answer 1

y = 2.8t + 9.8t²/2 = 48; 4.9t² + 2.8t - 48 = 0; t = (-1.4 + √1.4² + 4.9·48)/4.9 = 2.86 s