# SOLUTION: A ball is thrown upward from the roof of a building 100m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m ?

Algebra ->  Algebra  -> Formulas -> SOLUTION: A ball is thrown upward from the roof of a building 100m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m ?       Log On

 Ad: Algebrator™ solves your algebra problems and provides step-by-step explanations! Ad: Algebra Solved!™: algebra software solves algebra homework problems with step-by-step help!

 Geometric and Other Formulas Answers archive In Depth

 Question 95055: A ball is thrown upward from the roof of a building 100m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m ? Answer by scott8148(6628)   (Show Source): You can put this solution on YOUR website!h=(-g/2)t^2+vt+s ... where g is gravitational acceleration (9.8 in meters), v is initial velocity, and s is starting height 80=-4.9t^2+20t+100 ... 0=-4.9t^2+20t+20 ... using quadratic equation gives ... t=-0.83 and t=4.91 ... the negative value is not realistic