physics cssa 04 ^_^ (1 Viewer)

[JimMcCool]

exactly what was the question asking?

 

[acmilan]

This is how i did it but i thought it was wrong when doing it.

It expels 1500kg/second so in 30 seconds it expels 45000kg. Therefore at 30seconds the mass of the rocket = 2000000 - 45000 = 1955000 kg.

a = F/m and F is always constant (cant remember the value of F)
a = F/1955000

Using the value that you get for a
The net force on the astronaut = 85 x a = in the 3000N range.

 

[steph@nie]

i should've studied. i made a long chain of the string used to tie books together and played with that for the last half hour... oh and I ate the curly wurly my teacher gave me. i made up a lot of stuff, but apparently some of it is right.. so yay.

 

[Premus]

i used force = T -mg ( thrust - mg)

T - mg = Ma

and ... a = (T-mg)/M
where M is the mass of the rocket after 30s

i got an answer somwhere around 40 N
......i think that the forces on astronauts are usually around 4 to 5 g

but i dont know if its right!

 

[acmilan]

I got my value for acceleration of the rocket at about 40 something ms^-2

 

[nomz]

i didn't know how to do that one either, but i did it the way acmilan1987 did it and got ~3487.9N which at the time i thought was way wrong

 

[JimMcCool]

what else did we have trouble with besides that and the resistor thing?

 

[Gesus]

wasnt it...

thrust = ma, where m = 1955000 from above and thrust was given
hence find a from that
then do F=ma + mg , where g= gravity and m = mass of astronaut (85kb), so the force on the astronuat was f = 85(9.8 +a) ?

otherwise im just stupid

 

[Li0n]

yeah same my accel/velcotiy was around 40 ms

but ffs i never learnt or done such type of questions
so i did
F = ma + mg
so what did me, (the idiot) do? i got the 8x10^7 force and added it to 85x9.8
ill still get afew marks seeming as i did the 30 second calcuation thing
but i had NFI for that question, i spent the rest of the time on it

 

[superbird]

acmilan1987 i also did it that way and got the same answer as you. I think we're probably at least half right.
Although is 3000N too strong for a human being to handle lol.
Also, wasnt the question asking about Force rather than g-force, i know they're kinda the same thing but still, i guess we could apply the F=ma equation here.
I am more concerned about the Kepler's Law of Periods question. what did people get for the value of v?

 

[jam3s]

acmilan1987 i also did it that way and got the same answer as you. I think we're probably at least half right.
Although is 3000N too strong for a human being to handle lol.
Also, wasnt the question asking about Force rather than g-force, i know they're kinda the same thing but still, i guess we could apply the F=ma equation here.
I am more concerned about the Kepler's Law of Periods question. what did people get for the value of v?

i got some thing close to the value given in the data sheet but it's still a bit off so i don;t know werid qestion

 

[Premus]

"I am more concerned about the Kepler's Law of Periods question. what did people get for the value of v?"

which question are u talking abt?

 

[townie]

does anybody else think there's waaaaay to much time for physics, i mean it basically equals 2 minutes a mark, which is a bit high when there are no essays and there are multiple choice q's. i finished the trials in 90 mins (althought we didnt have 2 do Q2Q)

PS. love our teacher, he gave us the formulas for the derrivation question, and changed the projectile question so it wasnt projected from a height

 

[superbird]

way too long? as if. it took me a while to get settled into the exam and gather my thoughts. thankgod its was 3 hours and not 2 as I would've been screwed.

 

[Li0n]

pfft 3 hours is good enough
you dream of getting perfect marks without 3 hours. seeming as your teacher left out your option topic and such, and some people like to 'perfect' their responses, 3 hours is good enough, if you like you can just sit back and look cool but others like to use their time wisely.
Cmon, its your last year you spent 12 years or whatever at school you may as well spend an extra hour trying. (my teacher said that, words of wisdom i say )

 

[Thomas_wow]

i couldnt do the question that asked what was the potential difference needed to allow the current to pass unobstructed through the magnetic field... didnt even try to do the question with the 20metre tower, confused the hell out of me. I derived the equation fine, but for some reason i got the escape velocity mixed up with the velocity of a satellite...

rest of questions were reasonable.

whoever asked who did medical physics, our school did. but our teacher changed the question sheet cause we had only done 1/2 of the topic.

saying that ill prolly get like 30% (as per usual)

 

[somborac]

My Teacher set the questions for Medical Physics so it was easy for me as i knew 90% of the stuff in medical, but he wouldnt tell us what he put in. However the rest of the stuff i done ok..i hope. In the train and lighetining i talked about time dilation which i believe is wrong. And for eddison and westinghouse i prob got full marks, coz its involves Nikola Tesla who is from my country. and the calculations i dont think i done good, but hopefully get the a mark or two for writing down a formula and attmpting the thing. but it was easier then i imagined.

 

[acmilan]

I got 100V for the potential difference question

 

[coroneos]

I got 100V for the potential difference question

same!!same!!

 

[Li0n]

im 100% sure 100v is correct
that was so stupid the question above basically hinted you what to do for the question below (i.e the thompson experiment)