Calculating Average Rate of Change for Related Rates Seesaw Problem

[stokes]

Homework Statement

A child weighs 34 Kg is seated on a seesaw. While a child who weighs 40 kg is situated on tghe opposite end of the seesaw. The functio B(x)= 34x / 40 gives the distance that the 40 kg child must sit from the center of the seesaw when the 34 kg child sits x meters from the center. The seesaw is 9m long find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters.

Homework Equations

I used the quotient rule to find the derivative of the function. Which turns out to be 68 / 80.

The Attempt at a Solution

I used the quotient rule to fine the instanenous rate of change which turns out to be B'(x)=
68/80.

I don't know how to takle the average rate of change.

 

[olgranpappy]

did you have a question?

 

[stokes]

The seesaw is 9m long find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters.

 

[rocomath]

Let's see some work, and this should be posted in the Calculus & Beyond subforum.

 

[olgranpappy]

"The seesaw is 9m long find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters."

that's not a question.

 

[stokes]

I used the quotient rule to fine the instanenous rate of change which turns out to be B'(x)=
68/80.

I don't know how to takle the average rate of change.

 

[stokes]

"The seesaw is 9m long find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters."

that's not a question.

Sorry...

 

[olgranpappy]

... that's okay, I guess. Two things:

1. 68/80 = 34/40 (you took a derivative of B with respect to x, not time...)

2. if you want to find an average rate, I think you might have to have a time somewhere in your problem. Was one given?

 

[stokes]

No it did not... It says find the average rate of change in distance.

 

[olgranpappy]

ah, okay. then I guess you have your answer.

 

[stokes]

Since it is over the interval of 1.5 and 2.5. Couldnt I find B(1.5) and B(2.5) and then find the average?

 

[stokes]

ah, okay. then I guess you have your answer.

I still did not get the answer... I am stuck...

 

[rocomath]

You're looking for the avg., not the instantaneous rate.

$$Rate_{avg}=B(x)=\frac{B(x_2)-B(x_1)}{x_2 -x_1}$$

 

[stokes]

The thing is the derivative is 34/40. Which equals to 0.85.

The prof gave us the answer which is -1.275. I haven't come close to that.

I've tried that formula before too...

I used...

f(x) = f(b) - f(a) / b-a

 

[stokes]

Please Help.

 

[olgranpappy]

I"m sorry, stokes. Your statement of the problem just doesn't make sense. I don't think anyone will be able to help you with this. Are you sure you are writing down all of the information in the problem exactly as given?

 

[stokes]

I am really sure I am writing everything down correctly.

 

[olgranpappy]

I am really sure I am writing everything down correctly.

So the statement of the problem in your text, or on your homework begins just as you wrote it:

"A child weighs 34 Kg is seated on a seesaw. While a child who weighs 40 kg is situated on tghe opposite end of the seesaw. The functio B(x)= 34x / 40 gives the..."

Your text used the word "tghe"?

Your text used the word "functio"?

The first sentence seems to be missing words (perhaps an "and" in between "34 Kg" and "is")

Etc Etc Etc.

If you can't even take the time to write down the correct statement of the problem, then you should not expect to get much help here.

 

[stokes]

A child weighs 34 Kg is seated on a seesaw. While a child who weighs 40 kg is situated on the opposite end of the seesaw. The function B(x)= 34x / 40 gives the distance that the 40 kg child must sit from the center of the seesaw when the 34 kg child sits x meters from the center. The seesaw is 9m long find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters.

Im sorry I just reread my mistake.

 

[rocomath]

Your text used the word "tghe"?

Your text used the word "functio"?

Who cares, grow up.

Sorry no one is unable to help you at the moment stokes, just be patient and I'm sure someone may be able to.

 

[stokes]

Thanks.

 

[olgranpappy]

Who cares, grow up.

I care. There is no problem to be solved and no question to be answered. He hasn't given us the problem. He didn't take the time to write the damn thing down correctly and he can't expect anyone to be able to guess the missing pieces.

This is sounds like a very basic physics question and the solution should be trivial, but there is no solution because he hasn't stated the problem.

Sorry no one is unable to help you at the moment stokes, just be patient and I'm sure someone may be able to.

I think not.

 

[stokes]

I think I've stated it more then enough:

Find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters.

 

[rocomath]

I think I've stated it more then enough:

Find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters.

I think so too, and it's pretty immature for someone to attack your misspellings. Hope this doesn't stop you from coming here to ask for help :-]

 

[Rhae]

I've had this exact same question before...

You have to make the average rate of change chart...

Interval delta f(x) delta x delta f(x)/delta x
1.5m-2.5m 1.275-2.125= -.85 1 -.85


Hope that helps!

oh and I think your Prof gave you the wrong answer because ours gave us -.85 as the answer??

 

[rocomath]

oh and I think your Prof gave you the wrong answer because ours gave us -.85 as the answer??

Ah, that's the answer I initially got :-]