Question 192033
What you are trying to find is how long does it take the acorn to reach the ground where h = 0ft. (not h = 45ft., that's the initial height.), so...
{{{0 = -16t^2+45}}}
{{{16t^2 = 45}}}
{{{t^2 = 45/16}}}
{{{t = sqrt(45/16)}}}
{{{highlight(t = 1.677)}}}secs.