Solving Quadratic Functions - SAT Subject Test in Math II
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Question
A baseball is thrown straight up with an initial speed of 60 feet per second by a man standing on the roof of a 100-foot high building. The height of the baseball in feet as a function of time 
in seconds is modeled by the function
To the nearest tenth of a second, how long does it take for the baseball to hit the ground?
A baseball is thrown straight up with an initial speed of 60 feet per second by a man standing on the roof of a 100-foot high building. The height of the baseball in feet as a function of time
To the nearest tenth of a second, how long does it take for the baseball to hit the ground?
Answer
When the baseball hits the ground, the height is 0, so we set 
. and solve for 
.
This can be done using the quadratic formula:
Set 
:
One possible solution:
We throw this out, since time must be positive.
The other:
This solution, we keep. The baseball hits the ground in 5 seconds.
When the baseball hits the ground, the height is 0, so we set
This can be done using the quadratic formula:
Set
One possible solution:
We throw this out, since time must be positive.
The other:
This solution, we keep. The baseball hits the ground in 5 seconds.
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