posted by Kelly on .
If a ball is thrown off a 17.9m roof with the velocity of 23.9m/s and it takes 1.91sec to reach the ground, What is the horizontal displacement and the Velocity right before it hits the ground?
They don't tell you the angle (measured above horizontal) that the ball was thrown, but you can figure it out.
For a ball thrown horizontally, the distance fallen (vertically) is
Y = (g/2) t^2 = 17.9 m
Since that is also the height of the building, it WAS thrown horizontally. The horizontal velcoity component remains 23.9 m/s
Just multiply the initial velocity by the time of flight, to get the horizontal displacement.