Question that doesn't give you the radius of earth (1 Viewer)

[jamesfirst]

If a question states "altitude of ........" but doesn't give you the radius of Earth

Do I automatically assume that the radius of Earth is included with the altitude

 

[rawrence]

When you give an altitude of an object you don't add the radius of the Earth, altitude is the level above earth's surface.

Therefore if a question gives you altitude you have to add on Earth's radius

 

[jamesfirst]

But the radius of the Earth wasn't given in the question...

Why should we memorise that ?? It's not even on the data sheet

 

[Fizzy_Cyst]

But the radius of the Earth wasn't given in the question...

Why should we memorise that ?? It's not even on the data sheet

Really, they should gove it to you in the question as it is not in the data sheet. However, you can work it out from other constants given in the data sheet.

Use g = GM/r^2

 

[jamesfirst]

although I know g = GM/r^2

That formula is also not given in the formula sheet.... my teacher better not mark me wrong for not adding radius of earth,.........

 

[FCB]

If it wants the altitude then give them the altitude. For obvious reason, you wont get full marks if you give them the value without taking away the radius of the Earth.

 

[jamesfirst]

that's stupid because the radius of the earth wasn't given in the question .......... ==

 

[Fizzy_Cyst]

although I know g = GM/r^2

That formula is also not given in the formula sheet.... my teacher better not mark me wrong for not adding radius of earth,.........

But the 2 formulae you need to equate to come to that equation are definitely in the formula sheet =)

Of course the teacher will not give you full marks, as your answer is incorrect. I'm sure your teacher has said it a thousand times before, that altitude does not include the radius of the Earth. I know I do =)

Just take it as a learning experience, i'm sure you will remember this for next time now!

 

[alen180sx]

You should ask your teacher, because same thing happened to me in the half yearlies this year, there was a question about change in GPE, but our teacher had forgotten to add the radius of the earth, but he gave full marks for just doing final - initial, so if your logic was right you should get full marks.

 

[jamesfirst]

I knew about the radius of the Earth, and I know the 2 formulas to derive g = GM/r^2... although I know the formula

It's just that the question asked altitude of blah blah and I automatically assumed that radius of the Earth was included as it was NOT given in the data sheet nor in the question... it usually does in the HSC.

And yes my teacher did emphasise the importance of radius of the Earth

and I knew that in the exam... but I did a lot of past papers and all of them gave you the radius of the Earth hence I automatically assumed that the data given had the radius of the Earth included.

 

[FCB]

Asked my teacher and he said that you can write at the bottom of the page 'assumed radius was X meters' and then minused it from the value you obtained. He said that it allows the marker to recognize that you have seen that process.