SOLUTION: A ball is thrown upward from the roof of a building 100 m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m?
Algebra ->
Quadratic Equations and Parabolas
-> SOLUTION: A ball is thrown upward from the roof of a building 100 m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m?
Log On
Question 83818: A ball is thrown upward from the roof of a building 100 m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m? Answer by ankor@dixie-net.com(22740) (Show Source):
You can put this solution on YOUR website! A ball is thrown upward from the roof of a building 100 m tall with an initial velocity of 20 m/s. When will the ball reach a height of 80 m?
:
The equation for this: h(x) height and x = time in seconds
h(x) = -4.9x^2 + 20x + 100
:
To find time when ball is 80 m above the ground:
-4.9x^2 + 20x + 100 = 80
:
-4.9x^2 + 20x + 100 - 80 = 0
:
-4.9x^2 + 20x + 20 = 0
:
Solve for x to find the time (in seconds) it will be 80 ft above the ground
:
Use the quadratic formula; a=-4.9, b=20, c=20
: ; minus a minus = +
:
:
Do the math here you should get a positive solution of;
:
x = 4.9 seconds for it to be at 80 m
:
A graphical presentation of this event:
:
Notice that when x = 5 sec, it will be at about 80 meters (y)
Also notice that it will be 20 meters below the height of the building (x=0)
:
Did this make sense to you?
