HSC Physics Question Thread

[Whitey]

r ----> Radius of planetary body
d ----> Distance from the centre of a planetary body

Therefore they're the same thing

Thanks mate! This clarified the differences I had. I will now adjust my notes accordingly.

Welcome to the forums! Let us know if you need a hand finding stuff I'll let Jake know his slides are being put to good use!!

Thank you! Finding stuff shouldn't be too much of a hassle. The forums are neat so everything is easy to find, good job on your accessibility!

[Rathin]

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.

This is probably the hardest HSC physics can get in terms of relativity calculations. Good Luck

[Whitey]

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.

I'm no maths wizard and I haven't done much practice over the holidays, so I'm just having a crack. I'm thinking you have to use a combination of length and time contraction because light years is a distance and their travel speed is velocity? Or am I completely off track?

[katnisschung]

can someone pls run me through the working out
for this mass dilation question... its pretty simple but
i'm getting the wrong percentage

calculate the percentage increase in the mass of an Apollo rocket
as it escapes from Earth's gravity at 11.2 kp/s (yeahs i converted to m/s)

[Whitey]

can someone pls run me through the working out
for this mass dilation question... its pretty simple but
i'm getting the wrong percentage

calculate the percentage increase in the mass of an Apollo rocket
as it escapes from Earth's gravity at 11.2 kp/s (yeahs i converted to m/s)

I'm not expert, but I'll try to help. Is there an initial mass, because when I try to plug the numbers into the formula I have two unknown m values. Also just another thought of mine is that do you have to subtract 9.8 as gravity acts against the acceleration of the rocket?

[jakesilove]

can someone pls run me through the working out
for this mass dilation question... its pretty simple but
i'm getting the wrong percentage

calculate the percentage increase in the mass of an Apollo rocket
as it escapes from Earth's gravity at 11.2 kp/s (yeahs i converted to m/s)

I assume you mean kilometres per second? Well, we know that the mass dilation formula looks like



Where Mv is the mass of the fast-moving object, and Mo is the mass of the object at rest. Plugging our info into the equation (after converting to m/s) we get



If you solve this, you show that the change is mass is basically zero. Like, you get something like



Clearly, mass has increased, but by next to nothing. Did you type out the question correctly?

Jake

[katnisschung]

no there isn't an initial mass... i hypothetically let
m=1kg and then figured the percentage out as 1.0 x 10^-7%
but the answers says it 1.0x10^-8%

yeah i typed it correctly sighs our teacher gave us the old version of surfing

[jakesilove]

no there isn't an initial mass... i hypothetically let
m=1kg and then figured the percentage out as 1.0 x 10^-7%
but the answers says it 1.0x10^-8%

yeah i typed it correctly sighs our teacher gave us the old version of surfing

Interesting! Potentially the answers are wrong, but honestly you're so close that you clearly understand the material well enough

Also interesting that my answer is between yours and the solutions given in the book, but closer to yours

[katnisschung]

another question...

calculate the speed that would cause a length contraction of 15%...

[RuiAce]

another question...

calculate the speed that would cause a length contraction of 15%...

[beau77bro]

question: "calculate the altitude of a 500kg satellite which has a gravitational potential energy of 1.5x10^9J." im so bad at potential energy someone help ahhaha

[RuiAce]

question: "calculate the altitude of a 500kg satellite which has a gravitational potential energy of 1.5x10^9J." im so bad at potential energy someone help ahhaha

You could probably use mgh, but I never use that formula. Find it too unreliable.

[jamonwindeyer]

You could probably use mgh, but I never use that formula. Find it too unreliable.

I normally go with the \(E=mgh\) formula for altitudes under 1000km in this case, since the altitude is unknown, I'd say you made the best choice

[RuiAce]

I normally go with the \(E=mgh\) formula for altitudes under 1000km in this case, since the altitude is unknown, I'd say you made the best choice

Aha that's good to hear

I very rarely go to mgh though... don't trust its accuracy one bit

[beau77bro]

I normally go with the \(E=mgh\) formula for altitudes under 1000km in this case, since the altitude is unknown, I'd say you made the best choice

i think E = -Gm1m2/r won out i finally got the right answer... mostly because i miss calculated hahaha thankyou guys