# Complex word problem

• Oct 14th 2012, 11:12 AM
cluelessteenager101
Complex word problem
So, my precalculus teacher thinks that a class of about 28 students are all perfect masters of physics, therefore, she assumes that it's totally normal to give us a physics-related word problem -___- (90% of the class isn't involved/will never be involved with physics.) (Headbang) Here's the problem:

David threw a baseball into the air. The function of the height of the ball in feet is h = 80t –16t2, where t represents the time in seconds after the ball was thrown. Use this function to determine how long it took the ball to fall back to the ground.

Can someone help, please? I'm only a high school junior, and my teacher only gave a simple example to help out with this complex problem; the example and question don't even relate to one another the slightest bit.

Help? Thanks.
• Oct 14th 2012, 11:53 AM
MarkFL
Re: Complex word problem
Hint: set $h(t)=0$ and solve for $t$, taking the positive root. You already know that $t=0$ is one root, so if you divide through by $16t$, you will immediately have the other root.
• Oct 14th 2012, 11:53 AM
MaxJasper
Re: Complex word problem
(Shake)
• Oct 14th 2012, 12:06 PM
MarkFL
Re: Complex word problem
Completing the square on a quadratic would be a more appropriate precalculus technique of optimization. :)
• Oct 14th 2012, 01:23 PM
skeeter
Re: Complex word problem
Quote:

Originally Posted by cluelessteenager101
David threw a baseball into the air. The function of the height of the ball in feet is h = 80t –16t2, where t represents the time in seconds after the ball was thrown. Use this function to determine how long it took the ball to fall back to the ground.

when the ball hits the ground , h = 0 ... so much for the physics knowledge required to solve this problem.

0 = 80t - 16t2

factor ...

0 = 16t(5 - t)

t = 0 , t = 5

... now use some common sense to determine which solution applies.