# 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

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

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

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.

5. ## Re: HSC Physics Marathon 2017

Originally Posted by Rathin
I still get 139.89

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

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.

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°

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)

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

11. ## Re: HSC Physics Marathon 2017

derive the formula T = nBIA cos(theta)

12. ## Re: HSC Physics Marathon 2017

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

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...

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)

Q10.PNG

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.

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

Page 3 of 3 First 123

There are currently 1 users browsing this thread. (0 members and 1 guests)

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•