Sunday

December 21, 2014

December 21, 2014

Posted by **Audrey** on Friday, February 3, 2012 at 7:46am.

a ball is thrown straight down from the top of a 220 feet building with an initital velocity of -22ft/s. What is the velocity of the ball after 3 seconds? What is the velocity of the ball after falling 108 feet?

2. Relevant equations

s(t) = -16t^2 + Vi(t) + si vi = initial velocity, si = initial position

3. The attempt at a solution

s(t) = -16t^2 +Vi(t) +si

= -16t^2 - 22ft/s + 200ft

V(t) = -32(t) - 22ft/s

V(3) = -96 ft/s - 22ft/s = -118 ft/s

I can seem to figure out how to determine the velocity of the ball after it has dropped 108ft.

I should be able to do this, but i'm missing something, somewhere on what should be pretty basic.

Thanks for any guidance!

- Calculus -
**Reiny**, Friday, February 3, 2012 at 9:00amYour equation

s(t) = 16t^2 - 22t + 220 is correct and tells you

how high the object is at any time t

But they are asking for the velocity after it has fallen 108 feet, not when it is 108 feet high

It started at 220, so after falling 108 feet, the height will be 112

so 112 = -16t^2 - 22t + 220

16t^2 + 22t - 108 = 0

t = (-22 ± √7396)/32

= 2 or a negative, (ahhh, it would have factored)

so take v(2) , that should give you the answer you need

check:

when t=0 , s(0) = 220 -- it has fallen 0 feet

when t=1 , s(1) = 182 -- it has fallen 38 ft

when t=2 , s(2) = 112 -- it has fallen 108 ft

**Answer this Question**

**Related Questions**

Math, Please Help!!! - 1. The problem statement, all variables and given/known ...

Calculus - A ball is thrown straight down from the top of a 220-foot building ...

Physical Science - Four balls are taken to the top of a building. Ball 1 is ...

Physics - Ball A is thrown straight down off the top of a tall building with an ...

Calculus - When a ball is thrown straight down from the top of a tall building, ...

12th Grade Calculus - When a ball is thrown straight down from the top of a tall...

Math: Word Problem - A ball is thrown upward from the top of a building which is...

Math - A ball is thrown downward from the top of a 100-foot building with an ...

Physics - Two baseballs are thrown off the top of a building that is 7.24 m high...

math - a ball is thrown upward at 64 feet per second from the top of an 80 feet ...