• Got a question on how to use our new website? Check out our user guide here!

GPE question (1 Viewer)

I97

Active Member
Joined
Jan 23, 2014
Messages
110
Gender
Male
HSC
2015
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
11216382_10205484881815516_1157585333_n.jpg
 

jackleung34

Member
Joined
May 7, 2014
Messages
74
Gender
Male
HSC
2015
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

Active Member
Joined
Jan 23, 2014
Messages
110
Gender
Male
HSC
2015
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

Member
Joined
Jul 17, 2014
Messages
61
Gender
Male
HSC
2015
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

Well-Known Member
Joined
Feb 11, 2013
Messages
1,853
Gender
Male
HSC
2014
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

New Member
Joined
May 22, 2015
Messages
1
Gender
Male
HSC
2015
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.


Sent from my iPad using Tapatalk
 

InteGrand

Well-Known Member
Joined
Dec 11, 2014
Messages
6,090
Gender
Male
HSC
N/A
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.


Sent from my iPad using Tapatalk
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.
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top