A free fall A girl standing on a bridge drops a stone. If it takes 5.25 s for the stone to hit the water below, what is the girl's distance above the water? what speed does the stone hit the water?

Answer 1

One of the free-fall kinematic equations of motion is:

y = v_it + 1/2gt² where v_i is the initial velocity (in this case since she "dropped" it, v_i = 0), g is the acceleration due to gravity (9.8 m/s²) and t is the time it takes to drop (in this case 5.25 s). So:

y = v_it + 1/2gt²

y = (0)(5.25) + 1/2(9.8)(5.25)²

y = 135 meters

Another of the free-fall kinematic equations of motion is:

v_f = v_i + gt where v_f is the final velocity, v_i is the initial velocity (in this case since she "dropped" it, v_i = 0), g is the acceleration due to gravity (9.8 m/s²) and t is the time it takes to drop (in this case 5.25 s). So:

v_f = v_i + gt

v_f = 0 + (9.8)(5.25)

v_f = 51.5 m/s