Question

If an object is dropped from a height of 85 feet, the function h(t)=-16t^2+85, gives the height of the object after t seconds approximately when will the object hit the ground

Answer 1

The object will hit the ground once the height equals to zero.


`h(t)=-16t^2+85 \\0=-16t^2+85 \\16t^2=85 \\t^2=(85)/(16) \\t=\sqrt{(85)/(16)}=\pm(√(85))/(4)`

The negative answer does not fit the condition of the problem
`\Rightarrow` the answer is
`(√(85))/(4)\approx2.31 \ seconds`.