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## #1 2017-08-27 06:42:57

Oran
Guest

### PreCalc Problems

I got these for homework and I'm not sure if they are solvable (might be missing some information)

An object is launched from a pad 25 feet off of the ground with a velocity of 350 feet per second. (Just this once I will tell you that the , where h is the height, g is gravity (32ft/s2 ,9.8m/s2) v0 is initial velocity and s is initial height)
a. Find the equation that represents the height of an object.
b. Use algebra to find the maximum height of the object. You must show all your work.
c. Use algebra to find how long the object is in the air.
d. State the domain and range

On the planet Persephone a soccer goalie kicks the ball from the ground. After 1 second the ball in 30 feet above the ground. The ball bounces on the ground after 4 seconds.
a. Write the height of the soccer ball as a function of time.
b. After how much time does the soccer ball hit the maximum height?
c. When is the soccer ball at 30 feet again?

How would I do these? I got a linear for the 1st question but it is supposed to be quadratic

## #2 2017-08-27 07:46:11

zetafunc
Moderator
Registered: 2014-05-21
Posts: 2,193
Website

### Re: PreCalc Problems

Hi Oran,

Have you considered registering an account with us?

Let's start with the first question. We'll work in feet since the question gives us the information in feet, rather than metres. What information do we have?

Let's take the upwards direction to be positive. We're given
,
, and
(that has a negative sign, because gravity acts downwards). So, at a time
, suppose that
is the height above the ground. We could use the equation
here, replacing
with
(because we start
feet above the ground), replacing
with
, and
with
. That'll give you a quadratic for
in terms of
. (You could also get one in terms of
, but judging by the question, I suspect this is how they might want you to do it.) How can you then use this equation to find the maximum height?

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## #3 2017-08-27 08:11:44

Oran2009
Member
Registered: 2016-06-13
Posts: 21

### Re: PreCalc Problems

Hi. I have solved the 2nd problem. But I still don't get the first question. How do I get the quadratic for h?

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## #4 2017-08-27 08:18:29

zetafunc
Moderator
Registered: 2014-05-21
Posts: 2,193
Website

### Re: PreCalc Problems

You could use the equation
and
with
, as detailed in post #2. This gives you a quadratic, which you can then solve to obtain the answer to the second part of that question.

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## #5 2017-08-27 11:19:43

Oran2009
Member
Registered: 2016-06-13
Posts: 21

### Re: PreCalc Problems

wait... So I got something like this when I substituted and simplified?

v^2 = 124100 - 64h

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## #6 2017-08-27 19:02:46

zetafunc
Moderator
Registered: 2014-05-21
Posts: 2,193
Website

### Re: PreCalc Problems

Yes, and how can you use that to find the maximum height?

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## #7 2017-08-28 02:12:39

Oran2009
Member
Registered: 2016-06-13
Posts: 21

I got it thanks!

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