# Where did I go wrong? (1 Viewer)

#### ohexploitable

##### hey
Calculate how far an astronaut would need to be away above the Earth in order for his weight to be 0.01 his weight on the Earth's surface.
$\bg_white \\0.01F=G\frac{Mm}{r^2}\\\\0.01mg=G\frac{Mm}{r^2}\\\\0.01g=G\frac{M}{r^2}\\\\r=\sqrt{G\frac{M}{0.01g}}\\\\r=6.39\times10^7\\\text{altitude}=6.39\times10^7-6378\times10^3\\\text{altitude}=5.75\times10^7$

Where did I go wrong?

#### Aquawhite

##### Retiring
What is your second last step involving, and what is the correct answer?

#### ohexploitable

##### hey
What is your second last step involving, and what is the correct answer?
The question asks "above the Earth" so I subtracted the radius of the Earth.

The correct answer is 1.93x105, however, it's from the Dot Point book which is plagued with incorrect answers.

#### Physics_FTW

##### New Member
The value you have gotten is correct for the question asked.

Easy way to check would be to sub in your 'r' value in the eqn 'g = GM/r^2'

Your r value comes out to a g of around 0.098 (which is 0.01 of g on earth)

Their r value comes out to a g of around 9.268. WRONG.

#### danjw

##### Member
I did the working and got the same answer as you, I also tried a different method and still got the same answer. I think you're right the book must be mistaken.

#### hscishard

##### Active Member
I got the same answer... and everything you did looks right . Need another person to determine if the book is wrong again

#### hscishard

##### Active Member
The value you have gotten is correct for the question asked.

Easy way to check would be to sub in your 'r' value in the eqn 'g = GM/r^2'

Your r value comes out to a g of around 0.098 (which is 0.01 of g on earth)

Their r value comes out to a g of around 9.268. WRONG.
I did the working and got the same answer as you, I also tried a different method and still got the same answer. I think you're right the book must be mistaken.
I got the same answer... and everything you did looks right . Need another person to determine if the book is wrong again
Yea