# A2 physics help

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#1
how do you go about these type of question

Two satellites, P and Q, of the same mass, are in circular orbits around the Earth. The radius of
the orbit of Q is three times that of P. Which one of the following statements is correct?
A The kinetic energy of P is greater than that of Q.
B The weight of P is three times that of Q.
C The time period of P is greater than that of Q.
D The speed of P is three times that of Q
0
3 months ago
#2
Go through each one and calculate if it's true or not. If you know only one is true or only one is false, you can stop once you find it.

In this case, knowing only one is true, you can probably just jump on A being the answer because you know P has to be going faster (and kinetic energy is just dependent on mass and speed). If you didn't know there was only one answer, you could also discount C based on that due to greater speed and shorter orbit definitely being shorter period. You can also discount the other two because the relationship between orbital radius and gravitational force (B) or orbital speed (D) is not linear.
1
#3
(Original post by ThomH97)
Go through each one and calculate if it's true or not. If you know only one is true or only one is false, you can stop once you find it.

In this case, knowing only one is true, you can probably just jump on A being the answer because you know P has to be going faster (and kinetic energy is just dependent on mass and speed). If you didn't know there was only one answer, you could also discount C based on that due to greater speed and shorter orbit definitely being shorter period. You can also discount the other two because the relationship between orbital radius and gravitational force (B) or orbital speed (D) is not linear.
I don't understand why not D if p has greater orbital speed because of the smaller orbital radius
0
3 months ago
#4
(Original post by MARTIANAlLIENS)
I don't understand why not D if p has greater orbital speed because of the smaller orbital radius
It is indeed faster, but not specifically 3. Do you know a formula relating orbital speed to the radius?
0
#5
(Original post by ThomH97)
It is indeed faster, but not specifically 3. Do you know a formula relating orbital speed to the radius?
𝐹 = 𝐺𝑚1𝑚2/𝑟^2 so F in inversely proportional to r^2
if r increases by three times then its (3r)^2 so 9r and therefore speed increases by 9 times
is this correct?
0
#6
(Original post by alice1wonderland)
Hi does anyone have jan 2021 physics edexcel ial unit 2 and 3 paper?
sorry no, i dont think its out yet.
0
3 months ago
#7
(Original post by MARTIANAlLIENS)
sorry no, i dont think its out yet.
okay thank you
0
3 months ago
#8
(Original post by MARTIANAlLIENS)
𝐹 = 𝐺𝑚1𝑚2/𝑟^2 so F in inversely proportional to r^2
if r increases by three times then its (3r)^2 so 9r and therefore speed increases by 9 times
is this correct?
That reasoning will rule out B (the weight option), and very similar (or stating the relationship between F and v) will rule out D.
0
#9
(Original post by ThomH97)
That reasoning will rule out B (the weight option), and very similar (or stating the relationship between F and v) will rule out D.
from what equation is there a relationship between F and V
0
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