A pinecone falls from a tree. The pinecone's height #y# (in feet) after #t# seconds can be modeled by #64-16t^2#. After how many seconds does the pinecone hit the ground?

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Answer 1 · 2017-12-28T20:36:04

2 seconds.

If y represent the height of the cone then:

#y=64-16t^2#

When the cone hits the floor the height will be #0#:

#64-16t^2=0#

Solve for #t#:

#16t^2=64#

#t^2=64/16=4#

#t=+-sqrt(4)=+-2#

Since we can't have negative time only #t=2# applies:

So the cone hits the ground after 2 seconds.