# Rational function helpp needed immedietly

1. Nov 2, 2009

### gamefreak

rational function helpp needed immedietly !!!!

1. when astraunauts go into space, they feel lighter. this is because weight decreases as a person rises above earth's gravitational pull according to the formula

W(h) = We/(1+h/6400)^2

where We is the person's weight in newtons, at sea level on earth and W(h) is the weight at h km above sea level

Q) at what range of altitudes will this astraunaut have a weight of less than 10 N?

2. Relevant equations

W(h) = We/(1+h/6400)^2

3. The attempt at a solution

i attempted it by trying various methods, it will take too long to type it up here and i already have the answer in the book i tried but i could not get that answer

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited: Nov 3, 2009
2. Nov 3, 2009

### n!kofeyn

Re: rational function helpp needed immedietly !!!!

W(h) is the weight of the person at a height of h above sea level. For this person to weigh less than 10 newtons, W(h) needs to be less than 10. So set W(h)<10 and solve for h.

3. Nov 3, 2009

### rock.freak667

Re: rational function helpp needed immedietly !!!!

Well you basically want to find when W(h)<10

so just solve for h in

$$\frac{820}{(1+\frac{h}{6400})^2}<10$$

4. Nov 3, 2009

### gamefreak

Re: rational function helpp needed immedietly !!!!

ok so when i solve that I end up with

82 (h+1)^2 > 0

im lost now?

5. Nov 3, 2009

### n!kofeyn

Re: rational function helpp needed immedietly !!!!

You didn't solve for h correctly. Hint: multiply both sides by (1+h/6400)2 and then take the square root of both sides.