if an acorn falls 45 feet from the top of the tree, how long will it take for the acorn to hit the ground.

Answer 1

Solve (1/2) g t^2 = 45 feet to get t.

g = 32.2 ft/s^2

Answer 2

Since this is a math question, I am surprised they did not tell you the formula to use. This is really a question about physics. They may be expecting you to use a formula with a different value of g.

The formula I gave you neglects air resistance, which would lengthen the time to fall by a small amount.