# Math Help - Struggling with Rate of Change for Rational Functions

1. ## Struggling with Rate of Change for Rational Functions

Hey guys, I've been googling for hours on how to solve this with no luck!

I need to find the average and instantaneous rate of change of a rational function:

As you get farther from Earth’s surface, gravity has less effect on you. For this reason, you actually weigh less at higher altitudes. A person who weighs 55kg can use the function:

W(h) = 6400(55)/ (h + 64000)

to find their weight, W in kgs, at a specific height, h in feet above sea level, above the Earth’s surface.

Find the average rate of change from heights of 750 ft to 1200 ft above sea level, and find the instantaneous rate of change at 1200 ft above sea level.

I know that average rate of change is [W(1200)-W(750)]/1200-750 right? But when I plug in values for h the answers aren't even close. I know I'm missing something but I just don't understand what!

The answer posted is -0.0065 but I get like -0.00008

2. Hello, OmegaCenturion!

I think you have a typo in the formula . . .

I need to find the average and instantaneous rate of change of a rational function:

As you get farther from Earth’s surface, gravity has less effect on you.
For this reason, you actually weigh less at higher altitudes.

A person who weighs 55 kg can use the function: . $W(h) \:=\: 6400\,\frac{55}{h + {\color{red}6400}}$

to find their weight, W in kgs, at a specific height, h in feet above sea level, above the Earth’s surface.

(a) Find the average rate of change from heights of 750 ft to 1200 ft above sea level.

(b) Find the instantaneous rate of change at 1200 ft above sea level.

Now try it . . .

3. Hi, I'm fairly positive I typed in the formula correctly, it was 64,000 not 6,400. Is it a matter of simply plugging in h values or is there some algebra involved? Perhaps I will post another question from the same worksheet as I'm unable to solve any of them

it looks like this:

6400(55)
________

h + 64,000

Airbags are a standard safety feature of most cars. Without airbags, a person or object would move forward at the velocity that the car is moving. A person inside a car traveling at 8m/s and weighing 8000kg would follow the function:

v (m)= [8000(m -1)] / [8000(m+1)] x 5

where m represents the mass of the person. Find the average rate of change as the mass of the person changes from 57 kg to 75 kg, and the
instantaneous rate of change at 75 kg.

How do you use that special notation? it would help a lot to know how to write like that

4. Can anyone help?