ATAR Notes: Forum

HSC Stuff => HSC Science Stuff => HSC Subjects + Help => HSC Physics => Topic started by: dermite on July 10, 2018, 01:39:11 pm

Title: GPE Qn: Help Needed
Post by: dermite on July 10, 2018, 01:39:11 pm: Hi There,

I am unsure of how to attempt this question, and would like help:
Title: Re: GPE Qn: Help Needed
Post by: jamonwindeyer on July 10, 2018, 09:50:09 pm: Hi dermite! This question has two stages:

1- We know that there is a 1MJ energy difference between the 10,000km and 20,000km orbits. So we can use that to find the $GMm$ constant (we don't need to know the individual values, because we never need to separate them in this question):

$1\times10^6=-\frac{GMm}{20,000\times10^3}--\frac{GMm}{10,000\times10^3}$

Solve that for $GMm$.

2- The work done to move the object from this new position to the 80,000km orbit is, again, just the difference between their GPE's:

$W=-\frac{GMm}{80,000\times10^3}--\frac{GMm}{20,000\times10^3}$

You know $GMm$ from above, so you can evaluate $W$! Hope it helps :)