Space ques... simple.... but not that easy ! (1 Viewer)

[asl2]

Space Ques...

---------------------------------------------------------------------------------
You have a mass of 60 Kg. Predict your "loss" in weight at the top of Sydney Tower, 305m above sea level
---------------------------------------------------------------------------------
The answer is 0.322 N

My method
* find the value of g ........ the g on earth I found using (g=GM/r^2) using the radius of the earth

* then i found the value of g at the top of the tower, earth radius + tower length.... very minor difference

* then found the weight of the person on earth using (w=mg) and the weight at the top of the tower,

* subtract the 2 answers and you get 0

so... this is obviously wrong !!!


Thanks

 

[kini mini]

Your method looks right to me. Check your working and the accuracy of the figures for the Earth's mass and radius.

 

[Marianna]

you may need to use more decimal places in your constants like don't round to the nearest whole number that kind of think

 

[t-i-m-m-y]

you probably get 0 because the change in weight is virtually negligible.. but ur method seems to be rite

 

[asl2]

I kept the values in the calculator memory because the difference was very subtle... but the answer surely can't be wrong either.... can someone try calculating it ?

Thx

 

[wogboy]

Hmm the weight difference W is,

W = GMm/r^2 - GMm/(r + h)^2
= GMm(1/r^2 - 1/(r + h)^2)

subbing:

G = 6.673E(-11)
M = 5.976E(24) Kg
m = 60 Kg
r = 6378000 m
h = 305m,

we get:

W = 6.673E(-11) * 5.976E(24) * 60 * {1/(6378000)^2 - 1/(6378305)^2} N

= 0.05625 N

(make sure to use your calculator's memory for storing parts of the equation, not writing them down and rounding them off and then multiplying together)

which seems to contradict the answer of 0.322 N. So maybe the textbook is wrong?

 

[kini mini]

Originally posted by wogboy

we get

<snip>
= 0.05625 N

(make sure to use your calculator's memory for storing parts of the equation, not writing them down and rounding them off and then multiplying together)

which seems to contradict the answer of 0.322 N. So maybe the textbook is wrong?

I get the same thing using your figures wogboy , was too lazy to look them up myself .

I notice you used 4sf as well so we shouldn't have an accuracy problem...perhaps a bizarre rounding error in the textbook??

 

[t-i-m-m-y]

hey!
textbooks are quite often wrong with answers

 

[tt_j65]

Originally posted by t-i-m-m-y
hey!
textbooks are quite often wrong with answers

especially longman

i did the first maths question in the space chapter and there was a t/e in the answer pdf that was on the cd

 

[Constip8edSkunk]

i dun even have the cd stupid teacher resources only

However Macmillan is so much worse....