Physics Predictions/Thoughts (2 Viewers)

[p711]

so what do I sub in for r in U? 6800km or 42000km

cuz its change in energy so its final - initial

 

[p711]

but what i don't understand about using total energy is when you do final - initial u will get half of the answer ? (unless im doing sum wrong i do believe the right way is to do uf-ui) coz, when u do -gmm/2r(final) - (-gmm/2r(initial) you will get -gmm/2r(final) + gmm/2r(inital) which is half of answer a? can someone like legit go through the steps cause im bugging i think

 

[Goldattacker40000]

so what do I sub in for r in U? 6800km or 42000km

BOTHHH.
∆E=1/2Uf-1/2Ui
=-GMm/2rf - (-GMm/2ri)

 

[Trippzy]

but what i don't understand about using total energy is when you do final - initial u will get half of the answer ? (unless im doing sum wrong i do believe the right way is to do uf-ui) coz, when u do -gmm/2r(final) - (-gmm/2r(initial) you will get -gmm/2r(final) + gmm/2r(inital) which is half of answer a? can someone like legit go through the steps cause im bugging i think

ur logic is right but maybe u subbed in wrong or calculated wrong. i got A now

 

[Trippzy]

BOTHHH.
∆E=1/2Uf-1/2Ui
=-GMm/2rf - (-GMm/2ri)

damn bro relax thanks for ur help i understand now

 

[Goldattacker40000]

but what i don't understand about using total energy is when you do final - initial u will get half of the answer ? (unless im doing sum wrong i do believe the right way is to do uf-ui) coz, when u do -gmm/2r(final) - (-gmm/2r(initial) you will get -gmm/2r(final) + gmm/2r(inital) which is half of answer a? can someone like legit go through the steps cause im bugging i think

∆E=-(6.67x10^-11x1000x6.0x10^23)/(2x42000x10^3)-(-6.67x10^-11x1000x6x10^24)/(2x6800x10^3)
=the answer in A cant be bothered seeing what it was

 

[Yueyue]

cant u just use Ufinal - Uinitial? I did that and got the same answer A

You only use that when they ask for work done. In this case, the change in energy refers to change in TOTAL energy

 

[p711]

∆E=-(6.67x10^-11x1000x6.0x10^23)/(2x42000x10^3)-(-6.67x10^-11x1000x6x10^24)/(2x6800x10^3)
=the answer in A cant be bothered seeing what it was

so we dont add radius of the earth? otherwise then i agree the answer is a.

 

[Yueyue]

so we dont add radius of the earth? otherwise then i agree the answer is a.

The question states radius, not altitude so you don’t have to add it

 

[Trippzy]

so we dont add radius of the earth? otherwise then i agree the answer is a.

no because the radius is from the centre of the earth. when it says altitude that's when u add radius

 

[p711]

yo im a next level retard nvm

 

[Trippzy]

You only use that when they ask for work done. In this case, the change in energy refers to change in TOTAL energy

yea thanks for the help

 

[scacredcat]

just remember guys: Orlando Bloom And Fergie Gonna Kill Me

also guys good luck, this has been so majorly stressful but the camaraderie and the feeling that I'm not the only one who's screwed for this has really helped out heaps so thank you. also for most of us this is our last exam, we finally made it!! regardless of our results the fact that we were all able to get through this hellish month is amazing and I think the government should give us all a million dollars for it and then leave us to go live in the mountains with the giant panda snails

 

[_DidntStudyForEnglish]

If i were to use 9.81 for acceleration due to gravity instead of 9.8 will they care??

 

[Yueyue]

If i were to use 9.81 for acceleration due to gravity instead of 9.8 will they care??

I wouldn’t risk it since the data sheet has 9.8 on it

 

[scacredcat]

If i were to use 9.81 for acceleration due to gravity instead of 9.8 will they care??

I mean on the reference sheet it says 9.8 so maybe just use that

 

[carrotsss]

If i were to use 9.81 for acceleration due to gravity instead of 9.8 will they care??

whats the point

 

[_DidntStudyForEnglish]

whats the point

because it generally is the more used value out of the two

 

[carrotsss]

because it generally is the more used value out of the two

the hsc syllabus uses 9.8, so you use 9.8. if they wanted you to use 9.81 they'd give you 9.81

 

[Trippzy]

guys do u reckon i sack learning 8.5 standard model or just do practice questions for all modules