GPE question (1 Viewer)

[I97]

Hi,
Could someone please explain why B is the supposedly correct answer and not D. The explanation was that reference is taken from the Earth's centre but from my understanding of GPE, a point at infinity is taken to be 0.
Thanks

 

[jackleung34]

Your understanding is correct, and i suppose the explanation makes sense. However, the question doesn't prompt you to consider it from the earths F.O.R. so this shit is fucked. Where'd you get this Q

 

[I97]

Half yearly. That's the thing i'm not quite sure why you need to take the earth as the F.O.R as it is not explicitly suggested in the question and is phrased pretty much like most other GPE questions where the graph for D would be used.

 

[p0llex]

I don't see how B can be the answer:

Firstly GPE is always negative and approaches 0 as the distance approaches infinity, as shown in D.
Secondly the change in GPE should be greatest when the asteroid is close to the earth. B shows the asteroid having almost no change near earth and quickly approaching infinite GPE when it's far away, which makes no sense.

Have a talk to your teacher about it because it could just be a simple mistake on their part. For some example GPE graphs from the actual HSC which show the same shape as D have a look at:
27c of the 2014 paper
4 of the 2012 paper

 

[photastic]

Should be D. We know that GPE = - GMm/r , the greater the distance the higher the GPE as it will approach zero since we take infinite the point where GPE will equal to zero.

 

[dmcstravick]

It's b, at the furthest distance (infinite) the GPE is 0, as the distance gets greater the potential energy increases till an infinite distance.


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[InteGrand]

It's b, at the furthest distance (infinite) the GPE is 0, as the distance gets greater the potential energy increases till an infinite distance.


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Gravitational potential energy should always be negative assuming we use an infinite distance as the reference 0 point. So it can't be B, if we assume that.