# Thread: HSC Physics Marathon 2017

1. ## Re: HSC Physics Marathon 2017

F(G on surface)= (6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3)^2)=758.16N
F(G inside satellite) =(6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3 +685x10^3)^2)=618.27N
ΔF(G)= 618.27-758.16=-139.89N
=138.89N opposite the direction of the center of Earth  Reply With Quote

2. ## Re: HSC Physics Marathon 2017 Originally Posted by Rathin F(G on surface)= (6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3)^2)=758.16N
F(G inside satellite) =(6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3 +685x10^3)^2)=618.27N
ΔF(G)= 618.27-758.16=-139.89N
=138.89N opposite the direction of the center of Earth
not a big mistake but it's 138.89 in the second last step  Reply With Quote

3. ## Re: HSC Physics Marathon 2017 Originally Posted by Commando007 not a big mistake but it's 138.89 in the second last step
I still get 139.89  Reply With Quote

4. ## Re: HSC Physics Marathon 2017

Three moons X, Y and Z are in orbit around the same planet. The moons have identical orbital speeds and masses of M, 9M and 25M respectively. Determine the ratio of their orbital radii and justify your answer.  Reply With Quote

5. ## Re: HSC Physics Marathon 2017 Originally Posted by Rathin I still get 139.89
my bad
didnt read it carefully  Reply With Quote

6. ## Re: HSC Physics Marathon 2017 Originally Posted by Rathin Three moons X, Y and Z are in orbit around the same planet. The moons have identical orbital speeds and masses of M, 9M and 25M respectively. Determine the ratio of their orbital radii and justify your answer.
The ratio is just 1:1:1 as orbital radii --> identical for all three moons (since the orbital speed and orbital does not depend on the mass).
When Fc = Fg
where Fc = (mv^2)/2 -------- and Fg = (GmMp)/r^2 )where Mp is the mass of the planet)

ending up with r = (GMp)v^2 (masses cancel out so the orbital speed and orbital radii does not depend on the mass) and r is constant in this case
THEREFORE the ratio is 1:1:1  Reply With Quote

7. ## Re: HSC Physics Marathon 2017

So I'm a bit stumped on how to find the launch speed and angle of launch from the horizontal. I'm given the Horizontal component which is 30 ms^-1 and the vertical component which is 80 ms^-1.  Reply With Quote

8. ## Re: HSC Physics Marathon 2017 Originally Posted by dragon658 So I'm a bit stumped on how to find the launch speed and angle of launch from the horizontal. I'm given the Horizontal component which is 30 ms^-1 and the vertical component which is 80 ms^-1.
u(y)=80m/s
u(x)=30m/s

by Pythagoras theorem
∴|u|=√(u(y)^2)+(u(x)^2))
∴|u|=√80^2+30^2
∴|u|≈85.44m/s
θ (below horizontal) = tan^-1(u(y)/u(x))
∴θ=tan^-1(80/30)
∴θ≈69°  Reply With Quote

9. ## Re: HSC Physics Marathon 2017

A golf ball was smashed at 25ms^-1 and at a angle of 40 degrees
a) find the total time it took for the ball to bounce (2 marks)
b) find range (2 marks)  Reply With Quote

10. ## Re: HSC Physics Marathon 2017 Originally Posted by Commando007 A golf ball was smashed at 25ms^-1 and at a angle of 40 degrees
a) find the total time it took for the ball to bounce (2 marks)
b) find range (2 marks)
y=25tsin40-4.9t^2
x= 25tcos40
t= 3.28s

Range = 62.8m  Reply With Quote

11. ## Re: HSC Physics Marathon 2017

derive the formula T = nBIA cos(theta)  Reply With Quote

12. ## Re: HSC Physics Marathon 2017

Compare the inertial and non-inertial frame of references. (3)  Reply With Quote

13. ## Re: HSC Physics Marathon 2017 Originally Posted by JackPatel derive the formula T = nBIA cos(theta)
I can only think of equating F = nBIL and F = T/d to get nBIL = T/d, T = nBILd (and L*d = Area of rectangle/square) and you just add in the cos theta as the angle between the plane of the coil and the magnetic field... something like that... Originally Posted by Rathin Compare the inertial and non-inertial frame of references. (3)
I can't make a table on here so I'll just do dot points:
- Inertial frames are non-accelerating while non-inertial frames are accelerating.
- Inertial frames obey Newton's laws of classical mechanics while non-inertial frames do not.
- Inertial frames are accounted for by Einstein's special theory of relativity while non-inertial frames are accounted for by Einstein's general theory of relativity.
- Inertial frames obey Newton's first law and non-inertial frames have fictitious forces to explain motion caused by no net force, e.g. centrifugal force.

Should be enough for 3 marks I think...  Reply With Quote

14. ## Re: HSC Physics Marathon 2017

Outline how our understanding of time and space have changed since the publication of the theory of Special Relativity. How is this theory "Special"? (4 Marks)  Reply With Quote

15. ## Re: HSC Physics Marathon 2017

Q10.PNG

Help please! Thanks in advance!  Reply With Quote

16. ## Re: HSC Physics Marathon 2017

Its been a while!

CHALLENGE QUESTION

Every millennium Super Thuc and Super Brian fly to planet X to have a rap battle, which is 30 light years from their home planets. Planet Beast and Planet Guan respectively. But Thuc, having perfected his speed, travels at 0.8c whilst Brian only does 0.6c. How much older (or younger) will Thuc be then Brian.  Reply With Quote

17. ## Re: HSC Physics Marathon 2017 Originally Posted by Rathin Its been a while!

CHALLENGE QUESTION

Every millennium Super Thuc and Super Brian fly to planet X to have a rap battle, which is 30 light years from their home planets. Planet Beast and Planet Guan respectively. But Thuc, having perfected his speed, travels at 0.8c whilst Brian only does 0.6c. How much older (or younger) will Thuc be then Brian.
LOL THIS QUESTION! hahah  Reply With Quote

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