Originally Posted by

**Nikola** I need to know if there is a standard method of finding the answer to this. My exam is tomorrow and my teacher gave us a set of topics to study. This is titled Projectile Motion!

The question is:

The function h=-5t^2 + 20t + 2 gives the approximate height, h meters of a trown football as a function of the time, t seconds since it was thrown. The ball hit the ground before the receiver could get near it.

a) How long was the ball in the air, to the nearest tenth of a second?

b) for how many seconds was the height of the ball at least 17 m?

The answers are:

a) 4.1

b) 2

I dont understand how to get the answers though. Sorry if there are misspelling in the question i had to rewrite it from the text book. Thanks again!